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                                                                     EXHIBIT 4.3

WHEN RECORDED
MAIL TO:

Gerald L. Waters
Union Electric Company
1901 Chouteau Avenue
St. Louis, MO 61303

- --------------------------------------------------------------------------------

                      Executed in 50 Counterparts, No. 28.

                             SUPPLEMENTAL INDENTURE

                              DATED AUGUST 15, 2002

                             UNION ELECTRIC COMPANY

                                       TO

                              THE BANK OF NEW YORK,
                                   AS TRUSTEE

                                    --------

     (SUPPLEMENTAL TO THE INDENTURE OF MORTGAGE AND DEED OF TRUST DATED
     JUNE 15, 1937, AS AMENDED, EXECUTED BY UNION ELECTRIC COMPANY TO
     THE BANK OF NEW YORK, AS TRUSTEE)

                                    --------

                       First Mortgage Bonds, Senior Notes
                                    Series AA

        This instrument was prepared by Steven R. Sullivan, Vice
        President, General Counsel and Secretary of Union
        Electric Company, 1901 Chouteau Avenue, St. Louis,
        Missouri 63103.

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     SUPPLEMENTAL INDENTURE, dated the 15th day of August, Two thousand and two
(2002) made by and between UNION ELECTRIC COMPANY, a corporation organized and
existing under the laws of the State of Missouri (hereinafter called the
"Company"), party of the first part, and The Bank of New York (successor trustee
to Bank of America, National Association, formerly Boatmen's Trust Company), a
bank existing under the laws of the State of New York (hereinafter called the
"Trustee"), as Trustee under the Indenture of Mortgage and Deed of Trust dated
June 15, 1937, hereinafter mentioned, party of the second part:

     WHEREAS, the Company has heretofore executed and delivered to the Trustee
its Indenture of Mortgage and Deed of Trust, dated June 15, 1937, as amended May
1, 1941, April 1, 1971, February 1, 1974, July 7, 1980 and February 1, 2000
(said Indenture of Mortgage and Deed of Trust as so amended, being hereinafter
referred to as the "Original Indenture"), to secure the payment of the principal
of and the interest (and premium, if any) on all bonds at any time issued and
outstanding thereunder, and indentures supplemental thereto dated June 15, 1937,
May 1, 1941, March 17, 1942, April 13, 1945, April 27, 1945, October 1, 1945,
April 11, 1947, April 13, 1949, September 13, 1950, December 1, 1950, September
20, 1951, May 1, 1952, March 1, 1954, May 1, 1955, August 31, 1955, April 1,
1956, July 1, 1956, August 1, 1957, February 1, 1958, March 1, 1958, November 5,
1958, March 16, 1959, June 24, 1959, December 11, 1959, August 17, 1960,
September 1, 1960, October 24, 1960, June 30, 1961, July 1, 1961, August 9,
1962, September 30, 1963, November 1, 1963, March 12, 1965, April 1, 1965, April
14, 1966, May 1, 1966, February 17, 1967, March 1, 1967, February 19, 1968,
March 15, 1968, August 21, 1968, April 7, 1969, May 1, 1969, September 12, 1969,
October 1, 1969, March 26, 1970, April 1, 1970, June 12, 1970, January 1, 1971,
April 1, 1971, September 15, 1971, December 3, 1973, February 1, 1974, April 25,
1974, February 3, 1975, March 1, 1975, June 11, 1975, May 12, 1976, August 16,
1976, April 26, 1977, October 15, 1977, November 7, 1977, December 1, 1977,
August 1, 1978, October 12, 1979, November 1, 1979, July 7, 1980, August 1,
1980, August 20, 1980, February 1, 1981, October 8, 1981, August 27, 1982,
September 1, 1982, December 15, 1982, March 1, 1983, June 21, 1984, December 12,
1984, June 11, 1985, March 1, 1986, May 1, 1986, May 1, 1990, December 1, 1991,
December 4, 1991, January 1, 1992, September 30, 1992, October 1, 1992, December
1, 1992, February 1, 1993, February 18, 1993, May 1, 1993, August 1, 1993,
October 1, 1993, January 1, 1994, and February 1, 2000, respectively, have
heretofore been entered into between the Company and the Trustee; and

     WHEREAS, Bonds have heretofore been issued by the Company under the
Original Indenture as follows:

          (1)  $80,000,000 principal amount of First Mortgage and Collateral
     Trust Bonds, 3 3/4% Series due 1962, all of which have been redeemed prior
     to the date of the execution hereof;

          (2)  $90,000,000 principal amount of First Mortgage and Collateral
     Trust Bonds, 3 3/8% Series due 1971, which are described in the
     Supplemental Indenture dated May 1, 1941 (hereinafter called the
     "Supplemental Indenture of May 1, 1941"), all of which have been paid at
     maturity prior to the date of the execution hereof;

          (3)  $13,000,000 principal amount of First Mortgage and Collateral
     Trust Bonds, 2 3/4% Series due 1975 (herein called the "Bonds of 1975
     Series"), which are described in the Supplemental Indenture dated October
     1, 1945 (hereinafter called the

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     "Supplemental Indenture of October 1, 1945"), all of which have been paid
     at maturity prior to the date of the execution hereof;

          (4)  $25,000,000 principal amount of First Mortgage and Collateral
     Trust Bonds, 2 7/8% Series due 1980 (herein called the "Bonds of 1980
     Series"), which are described in the Supplemental Indenture dated December
     1, 1950 (hereinafter called the "Supplemental Indenture of December 1,
     1950"), all of which have been paid at maturity prior to the date of the
     execution hereof;

          (5)  $30,000,000 principal amount of First Mortgage and Collateral
     Trust Bonds, 3 1/4% Series due 1982 (herein called the "Bonds of 1982
     Series"), which are described in the Supplemental Indenture dated May 1,
     1952 (hereinafter called the "Supplemental Indenture of May 1, 1952"), all
     of which have been paid at maturity prior to the date of the execution
     hereof;

          (6)  $40,000,000 principal amount of First Mortgage Bonds, 3 3/4%
     Series due 1986 (herein called the "Bonds of 1986 Series"), which are
     described in the Supplemental Indenture dated July 1, 1956 (hereinafter
     called the "Supplemental Indenture of July 1, 1956"), all of which have
     been paid at maturity prior to the date of the execution hereof;

          (7)  $35,000,000 principal amount of First Mortgage Bonds, 4 3/8%
     Series due 1988 (herein called the "Bonds of 1988 Series"), which are
     described in the Supplemental Indenture dated March 1, 1958 (hereinafter
     called the "Supplemental Indenture of March 1, 1958"), all of which have
     been paid at maturity prior to the date of the execution hereof;

          (8)  $50,000,000 principal amount of First Mortgage Bonds, 4 3/4%
     Series due 1990 (herein called the "Bonds of 1990 Series"), which are
     described in the Supplemental Indenture dated September 1, 1960
     (hereinafter called the "Supplemental Indenture of September 1, 1960"), all
     of which have been paid at maturity prior to the date of the execution
     hereof;

          (9)  $30,000,000 principal amount of First Mortgage Bonds, 4 3/4%
     Series due 1991 (herein called the "Bonds of 1991 Series"), which are
     described in the Supplemental Indenture dated July 1, 1961 (hereinafter
     called the "Supplemental Indenture of July 1, 1961"), all of which have
     been paid at maturity prior to the date of the execution hereof;

          (10) $30,000,000 principal amount of First Mortgage Bonds, 4 1/2%
     Series due 1993 (herein called the "Bonds of 1993 Series"), which are
     described in the Supplemental Indenture dated November 1, 1963 (hereinafter
     called the "Supplemental Indenture of November 1, 1963"), all of which have
     been redeemed prior to the date of the execution hereof;

          (11) $35,000,000 principal amount of First Mortgage Bonds, 4 1/2%
     Series due 1995 (herein called the "Bonds of 1995 Series"), which are
     described in the Supplemental Indenture dated April 1, 1965 (hereinafter
     called the "Supplemental Indenture of April 1, 1965"), all of which have
     been paid at maturity prior to the date of the execution hereof;

          (12) $30,000,000 principal amount of First Mortgage Bonds, 5 1/2%
     Series due 1996 (herein called the "Bonds of 1996 Series"), which are
     described in the Supplemental

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     Indenture dated May 1, 1966 (hereinafter called the "Supplemental Indenture
     of May 1, 1966"), all of which have been paid at maturity prior to the date
     of the execution hereof;

          (13) $40,000,000 principal amount of First Mortgage Bonds, 5 1/2%
     Series due 1997 (herein called the "Bonds of 1997 Series"), which are
     described in the Supplemental Indenture dated March 1, 1967 (hereinafter
     called the "Supplemental Indenture of March 1, 1967"), all of which have
     been paid at maturity prior to the date of the execution hereof;

          (14) $50,000,000 principal amount of First Mortgage Bonds, 7% Series
     due 1998 (herein called the "Bonds of 1998 Series"), which are described in
     the Supplemental Indenture dated March 15, 1968 (hereinafter called the
     "Supplemental Indenture of March 15, 1968"), all of which have been
     redeemed prior to the date of the execution hereof;

          (15) $35,000,000 principal amount of First Mortgage Bonds, 7 3/8%
     Series due 1999 (herein called the "Bonds of May 1999 Series"), which are
     described in the Supplemental Indenture dated May 1, 1969 (hereinafter
     called the "Supplemental Indenture of May 1, 1969"), all of which have been
     redeemed prior to the date of the execution hereof;

          (16) $40,000,000 principal amount of First Mortgage Bonds, 8 1/4%
     Series due 1999 (herein called the "Bonds of October 1999 Series"), which
     are described in the Supplemental Indenture dated October 1, 1969
     (hereinafter called the "Supplemental Indenture of October 1, 1969"), all
     of which have been redeemed prior to the date of the execution hereof;

          (17) $100,000,000 principal amount of First Mortgage Bonds, 9.95%
     Series due 1999 (herein called the "Bonds of November 1999 Series"), which
     are described in the Supplemental Indenture dated November 1, 1979
     (hereinafter called the "Supplemental Indenture of November 1, 1979"), all
     of which have been redeemed prior to the date of the execution hereof;

          (18) $60,000,000 principal amount of First Mortgage Bonds, 9% Series
     due 2000 (herein called the "Bonds of 2000 Series"), which are described in
     the Supplemental Indenture dated April 1, 1970 (hereinafter called the
     "Supplemental Indenture of April 1, 1970"), all of which have been redeemed
     prior to the date of the execution hereof;

          (19) $50,000,000 principal amount of First Mortgage Bonds, 7 7/8%
     Series due 2001 (herein called the "Bonds of January 2001 Series"), which
     are described in the Supplemental Indenture dated January 1, 1971
     (hereinafter called the "Supplemental Indenture of January 1, 1971"), all
     of which have been redeemed prior to the date of the execution hereof;

          (20) $50,000,000 principal amount of First Mortgage Bonds, 7 5/8%
     Series due 2001 (herein called the "Bonds of April 2001 Series"), which are
     described in the Supplemental Indenture dated April 1, 1971 (hereinafter
     called the "Supplemental Indenture of April 1, 1971"), all of which have
     been redeemed prior to the date of the execution hereof;

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          (21) $60,000,000 principal amount of First Mortgage Bonds, 8 1/8%
     Series due 2001 (herein called the "Bonds of October 2001 Series"), which
     are described in the Supplemental Indenture dated September 15, 1971
     (hereinafter called the "Supplemental Indenture of September 15, 1971"),
     all of which have been redeemed prior to the date of the execution hereof;

          (22) $70,000,000 principal amount of First Mortgage Bonds, 8 3/8%
     Series due 2004 (herein called the "Bonds of 2004 Series"), which are
     described in the Supplemental Indenture dated February 1, 1974 (hereinafter
     called the "Supplemental Indenture of February 1, 1974"), all of which have
     been redeemed prior to the date of the execution hereof;

          (23) $70,000,000 principal amount of First Mortgage Bonds, 10 1/2%
     Series due 2005 (herein called the "Bonds of 2005 Series"), which are
     described in the Supplemental Indenture dated March 1, 1975 (hereinafter
     called the "Supplemental Indenture of March 1, 1975"), all of which have
     been redeemed prior to the date of the execution hereof;

          (24) $70,000,000 principal amount of First Mortgage Bonds, 8 7/8%
     Series due 2006 (herein called the "Bonds of 2006 Series"), which are
     described in the Supplemental Indenture dated August 16, 1976 (hereinafter
     called the "Supplemental Indenture of August 16, 1976"), all of which have
     been redeemed prior to the date of the execution hereof;

          (25) $27,085,000 principal amount of First Mortgage Bonds, 5.80%
     Environmental Improvement Series 1977, which are described in the
     Supplemental Indenture dated October 15, 1977 (hereinafter called the
     "Supplemental Indenture of October 15, 1977"), all of which have been
     redeemed prior to the date of the execution hereof;

          (26) $60,000,000 principal amount of First Mortgage Bonds, 8 5/8%
     Series due 2007 (herein called the "Bonds of 2007 Series"), which are
     described in the Supplemental Indenture dated December 1, 1977 (hereinafter
     called the "Supplemental Indenture of December 1, 1977"), all of which have
     been redeemed prior to the date of the execution hereof;

          (27) $55,000,000 principal amount of First Mortgage Bonds, 9.35%
     Series due 2008 (herein called the "Bonds of 2008 Series"), which are
     described in the Supplemental Indenture dated August 1, 1978 (hereinafter
     called the "Supplemental Indenture of August 1, 1978"), all of which have
     been redeemed prior to the date of the execution hereof;

          (28) $60,000,000 principal amount of First Mortgage Bonds,
     Environmental Improvement Series 1980, which are described in the
     Supplemental Indenture dated August 1, 1980 (hereinafter called the
     "Supplemental Indenture of August 1, 1980"), all of which have been
     redeemed prior to the date of the execution hereof;

          (29) $150,000,000 principal amount of First Mortgage Bonds, 15 3/8%
     Series due 1991 (herein called the "Bonds of February 1991 Series"), which
     are described in the Supplemental Indenture dated February 1, 1981
     (hereinafter called the "Supplemental

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     Indenture of February 1, 1981"), all of which have been redeemed prior to
     the date of the execution hereof;

          (30) $125,000,000 principal amount of First Mortgage Bonds, 15% Series
     due 1992 (herein called the "Bonds of 1992 Series"), which are described in
     the Supplemental Indenture dated September 1, 1982 (hereinafter called the
     "Supplemental Indenture of September 1, 1982"), all of which have been
     redeemed prior to the date of the execution hereof;

          (31) $100,000,000 principal amount of First Mortgage Bonds, 13% Series
     due 2013 (herein called the "Bonds of 2013 Series"), which are described in
     the Supplemental Indenture dated March 1, 1983 (hereinafter called the
     "Supplemental Indenture of March 1, 1983"), all of which have been redeemed
     prior to the date of the execution hereof;

          (32) $100,000,000 principal amount of First Mortgage Bonds, 9 3/8%
     Series due 2016 (herein called the "Bonds of 2016 Series"), which are
     described in the Supplemental Indenture dated March 1, 1986 (hereinafter
     called the "Supplemental Indenture of March 1, 1986"), all of which have
     been redeemed prior to the date of the execution hereof;

          (33) $100,000,000 principal amount of First Mortgage Bonds, 8 7/8%
     Series due 1996 (herein called the "Bonds of 1996 Series"), which are
     described in the Supplemental Indenture dated May 1, 1986 (hereinafter
     called the "Supplemental Indenture of May 1, 1986"), all of which have been
     redeemed prior to the date of the execution hereof;

          (34) $60,000,000 principal amount of First Mortgage Bonds,
     Environmental Improvement Series 1990A, which are described in the
     Supplemental Indenture dated May 1, 1990 (hereinafter called the
     "Supplemental Indenture of May 1, 1990"), all of which have been redeemed
     prior to the date of the execution hereof;

          (35) $125,000,000 principal amount of First Mortgage Bonds, 8 3/4%
     Series due 2021 (herein called the "Bonds of 2021 Series"), which are
     described in the Supplemental Indenture dated December 1, 1991 (hereinafter
     called the "Supplemental Indenture of December 1, 1991"), all of which are
     outstanding at the date of the execution hereof;

          (36) $75,000,000 principal amount of First Mortgage Bonds, 8.33%
     Series due 2002 (herein called the "Bonds of 2002 Series"), which are
     described in the Supplemental Indenture dated December 4, 1991 (hereinafter
     called the "Supplemental Indenture of December 4, 1991"), all of which are
     outstanding at the date of the execution hereof;

          (37) $100,000,000 principal amount of First Mortgage Bonds, 7.65%
     Series due 2003 (herein called the "Bonds of 2003 Series"), which are
     described in the Supplemental Indenture dated January 1, 1992 (hereinafter
     called the "Supplemental Indenture of January 1, 1992"), all of which are
     outstanding at the date of the execution hereof;

          (38) $204,000,000 aggregate principal amount of First Mortgage Bonds,
     consisting of $100,000,000 principal amount of 6 3/4% Series due 1999 and

                                        5
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     $104,000,000 principal amount of 8 1/4% Series due 2022 (herein called the
     "Bonds of 1999 Series" and "Bonds of 2022 Series", respectively), which are
     described in the Supplemental Indenture dated October 1, 1992 (hereinafter
     called the "Supplemental Indenture of October 1, 1992"), of which the Bonds
     of 1999 Series have been paid at maturity prior to the date of execution
     hereof and the Bonds of 2022 Series are outstanding at the date of the
     execution hereof;

          (39) $170,000,000 aggregate principal amount of First Mortgage Bonds,
     consisting of $85,000,000 principal amount of 7 3/8% Series due 2004 and
     $85,000,000 principal amount of 8% Series due 2022 (herein called the
     "Bonds of December 2004 Series" and "Bonds of December 2022 Series",
     respectively, which are described in the Supplemental Indenture dated
     December 1, 1992, (hereinafter called the "Supplemental Indenture of
     December 1, 1992), all of which are outstanding at the date of the
     execution hereof;

          (40) $188,000,000 principal amount of First Mortgage Bonds, 6 7/8%
     Series due 2004 (herein called the "Bonds of August 2004 Series"), which
     are described in the Supplemental Indenture dated February 1, 1993
     (hereinafter called the "Supplemental Indenture of February 1, 1993"), all
     of which are outstanding at the date of the execution hereof;

          (41) $148,000,000 principal amount of First Mortgage Bonds, 6 3/4%
     Series due 2008 (herein called the "Bonds of May 2008 Series"), which are
     described in the Supplemental Indenture dated May 1, 1993 (hereinafter
     called the "Supplemental Indenture of May 1, 1993"), all of which are
     outstanding at the date of the execution hereof;

          (42) $75,000,000 principal amount of First Mortgage Bonds, 7.15%
     Series due 2023 (herein called the "Bonds of 2023 Series"), which are
     described in the Supplemental Indenture dated August 1, 1993 (hereinafter
     called the "Supplemental Indenture of August 1, 1993"), all of which are
     outstanding at the date of the execution hereof;

          (43) $44,000,000 principal amount of First Mortgage Bonds,
     Environmental Improvement Series 1993 (herein called the "Bonds of 2028
     Series"), which are described in the Supplemental Indenture dated October
     1, 1993 (hereinafter called the "Supplemental Indenture of October 1,
     1993"), all of which are outstanding at the date of the execution hereof;
     and

          (44) $100,000,000 principal amount of First Mortgage Bonds, 7% Series
     due 2024 (herein called the "Bonds of 2024 Series"), which are described in
     the Supplemental Indenture dated January 1, 1994 (hereinafter called the
     "Supplemental Indenture of January 1, 1994"), all of which are outstanding
     at the date of the execution hereof;

and

     WHEREAS, the Company on August 31, 1955 acquired all of the properties of
Union Electric Power Company, the Subsidiary as defined in Article I of the
Original Indenture, upon the dissolution of the Subsidiary; the Company, by
Supplemental Indenture dated August 31, 1955, conveyed all of the properties so
acquired (other than property of the character defined as excepted property in
the granting clauses of the Original Indenture) to the Trustee upon the terms

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and trusts in the Original Indenture and the indentures supplemental thereto set
forth for the equal and proportionate benefit and security of all present and
future holders of the Bonds and coupons issued and to be issued thereunder, all
the shares of stock of the Subsidiary were released from the lien of the
Original Indenture; and the Company became entitled to change the general
designation of the Bonds so as to omit the words "and Collateral Trust"; and

     WHEREAS, the Articles of Incorporation of the Company were duly amended on
April 23, 1956, to change its corporate name from "Union Electric Company of
Missouri" to "Union Electric Company"; and

     WHEREAS, the Articles of Agreement of the Trustee were duly amended
effective on January 4, 1982 to change its corporate name from "St. Louis Union
Trust Company" to "Centerre Trust Company of St. Louis", and further amended on
December 9, 1988, to change its corporate name from "Centerre Trust Company of
St. Louis" to "Boatmen's Trust Company"; and

     WHEREAS, that on March 13, 1998, Boatmen's Trust Company merged into
NationsBank, National Association and effective July 5, 1999, changed its name
to Bank of America, National Association; and

     WHEREAS, that on February 1, 2000, The Bank of New York, as transferee of
the corporate trust business of Bank of America, National Association (formerly
known as Boatmen's Trust Company), Trustee under the Original Indenture, became
successor Trustee under the Original Indenture; and

     WHEREAS, the Company is entitled at this time to have authenticated and
delivered additional Bonds on the basis of "refundable bonds" upon compliance
with and pursuant to the provisions of Section 6 of Article III of the Original
Indenture; and

     WHEREAS, the Company has entered into an Indenture dated as of August 15,
2002 (the "Senior Note Indenture") with The Bank of New York, as trustee (the
"Senior Note Trustee") providing for the issuance from time to time of senior
notes thereunder; and

     WHEREAS, the Company desires by this Supplemental Indenture to provide for
the creation of, and the issuance to the Senior Note Trustee of, a new series of
Bonds under the Original Indenture as security for $173,000,000 aggregate
principal amount of the Company's 5.25% Senior Secured Notes due 2012 (the
"Senior Notes") to be issued under the Senior Note Indenture, to have the
designation provided in Article I, Section 1 hereof (herein called the "New
Bonds"), and the Original Indenture provides that certain terms and provisions,
as determined by the Board of Directors of the Company, of the Bonds of any
particular series may be expressed in and provided by the execution of an
appropriate supplemental indenture; and

     WHEREAS, the Company also desires by this Supplemental Indenture to amend
the provisions of Article XV of the Original Indenture to establish new
procedures concerning amendments thereof, as set forth in Article VI hereof; and

     WHEREAS, the Original Indenture provides that the Company and the Trustee
may enter into indentures supplemental to the Original Indenture specifically to
convey, transfer and assign to the Trustee and to subject to the lien of the
Original Indenture additional properties acquired by the Company; and

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     WHEREAS, the Company, in the exercise of the powers and authority conferred
upon and reserved to it under the provisions of the Original Indenture and
pursuant to appropriate resolutions of the Board of Directors, has duly resolved
and determined to make, execute and deliver to the Trustee a Supplemental
Indenture in the form hereof for the purposes herein provided; and

     WHEREAS, all conditions and requirements necessary to make this
Supplemental Indenture a valid, binding and legal instrument have been done,
performed and fulfilled and the execution and delivery hereof have been in all
respects duly authorized;

     NOW, THEREFORE, THIS INDENTURE WITNESSETH:

     That, in consideration of the premises and of the mutual covenants herein
contained and of the acceptance of this trust by the Trustee and of the sum of
One Dollar duly paid by the Trustee to the Company at or before the time of the
execution of this Supplemental Indenture, and of other valuable considerations,
the receipt whereof is hereby acknowledged, and in order further to secure the
payment of the principal of and interest (and premium, if any) on all Bonds at
any time issued and outstanding under the Original Indenture, according to their
tenor and effect, and to secure the Senior Notes, the Company has executed and
delivered this Supplemental Indenture and has granted, bargained, sold,
warranted, aliened, remised, released, conveyed, assigned, transferred,
mortgaged, pledged, set over and confirmed and by these presents does grant,
bargain, sell, warrant, alien, remise, release, convey, assign, transfer,
mortgage, pledge, set over and confirm unto The Bank of New York, as Trustee,
and to its successors in trust under the Original Indenture forever, all and
singular the following described properties (in addition to all other properties
heretofore subjected to the lien of the Original Indenture and not heretofore
released from the lien thereof) - that is to say:

                                        8
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                                     FIRST.

     ALL power houses, plants, buildings and other structures, dams, dam sites,
substations, heating plants, gas works, holders and tanks, together with all and
singular the electric, heating, gas and mechanical appliances appurtenant
thereto of every nature whatsoever, now owned by the Company, including all and
singular the machinery, engines, boilers, furnaces, generators, dynamos,
turbines and motors, and all and every character of mechanical appliance for
generating or producing electricity, steam, gas and other agencies for light,
heat, cold, or power or other purposes, and all transmission and distribution
systems used for the transmission and distribution of electricity, steam, gas
and other agencies for light, heat, cold or power or any other purpose
whatsoever, whether underground or overhead, surface or otherwise, now owned by
the Company, including all poles, towers, posts, wires, cables, conduits,
manholes, mains, pipes, tubes, drains, furnaces, switchboards, transformers,
conductors, insulators, supports, meters, lamps, fuses, junction boxes,
regulator stations, and other electric, steam and gas fixtures and apparatus;
all of the aforementioned property being located in the City of St. Louis, the
counties of Adair, Audrain, Benton, Bollinger, Boone, Butler, Caldwell,
Callaway, Camden, Cape Girardeau, Clark, Clay, Clinton, Cole, Cooper, Crawford,
Daviess, Dunklin, Franklin, Gasconade, Howard, Iron, Jefferson, Knox, Lewis,
Lincoln, Livingston, Macon, Madison, Maries, Marion, Miller, Mississippi,
Moniteau, Montgomery, Morgan, New Madrid, Osage, Pemiscot, Perry, Pettis,
Phelps, Pike, Pulaski, Ralls, Randolph, Ray, Reynolds, Ripley, St. Charles, St.
Francois, Ste. Genevieve, St. Louis, Saline, Schuyler, Scott, Stoddard, Warren,
Washington, and Wayne, Missouri, the counties of Adams, Alexander, Calhoun,
Franklin, Hancock, Henderson, Jackson, Jersey, Macoupin, Madison, Massac,
Monroe, Perry, Pike, Pulaski, St. Clair, Union, and Washington, Illinois, and
the counties of Des Moines, Henry, Johnson, Lee, and Washington, Iowa, upon real
estate owned by the Company, or occupied by it under rights to so occupy, which
real estate is described in the Indenture of Mortgage and Deed of Trust dated
June 15, 1937, in the Supplemental Indentures dated May 1, 1941, March 17, 1942,
April 13, 1945, April 27, 1945, October 1, 1945, April 11, 1947, April 13, 1949,
September 13, 1950, December 1, 1950, September 20, 1951, May 1, 1952, March 1,
1954, May 1, 1955, August 31, 1955, April 1, 1956, July 1, 1956, August 1, 1957,
February 1, 1958, March 1, 1958, November 5, 1958, March 16, 1959, June 24,
1959, December 11, 1959, August 17, 1960, September 1, 1960, October 24, 1960,
June 30, 1961, July 1, 1961, August 9, 1962, September 30, 1963, November 1,
1963, March 12, 1965, April 1, 1965, April 14, 1966, May 1, 1966, February 17,
1967, March 1, 1967, February 19, 1968, March 15, 1968, August 21, 1968, April
7, 1969, May 1, 1969, September 12, 1969, October 1, 1969, March 26, 1970, April
1, 1970, June 12, 1970, January 1, 1971, April 1, 1971, September 15, 1971,
December 3, 1973, February 1, 1974, April 25, 1974, February 3, 1975, March 1,
1975, June 11, 1975, May 12, 1976, August 16, 1976, April 26, 1977, October 15,
1977, November 7, 1977, December 1, 1977, August 1, 1978, October 12, 1979,
November 1, 1979, July 7, 1980, August 1, 1980, August 20, 1980, February 1,
1981, October 8, 1981, August 27, 1982, September 1, 1982, December 15, 1982,
March 1, 1983, June 21, 1984, December 12, 1984, June 11, 1985, March 1, 1986,
May 1, 1986, May 1, 1990, December 1, 1991, December 4, 1991, January 1, 1992,
September 30, 1992, October 1, 1992, December 1, 1992, February 1, 1993,
February 18, 1993, May 1, 1993, August 1, 1993, October 1, 1993, January 1,
1994, February 1, 2000 and in this Supplemental Indenture, or attached to or
connected with such real estate or transmission or distribution systems of the
Company leading from or into such real estate.

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                                     SECOND.

     ALSO, (except as in the Original Indenture expressly excepted) all
franchises and all permits, ordinances, easements, privileges, immunities and
licenses, all rights to construct, maintain and operate overhead, surface and
underground systems for the distribution and transmission of electricity, steam,
gas or other agencies for the supply to itself or others of light, heat, cold or
power, all rights-of-way, all waters, water rights and flowage rights and all
grants and consents, now owned or, subject to the provisions of Article XII of
the Original Indenture, which it may hereafter acquire.

     ALSO, (except as in the Original Indenture expressly excepted) all
inventions, patent rights and licenses of every kind now owned by the Company
or, subject to the provisions of Article XII of the Original Indenture, which it
may hereafter acquire.

                                     THIRD.

     ALSO, subject to the provisions of Article XII of the Original Indenture,
all other property, real, personal and mixed (except as therein or herein
expressly excepted) of every nature and kind and wheresoever situated now or
hereafter possessed by or belonging to the Company, or to which it is now, or
may at any time hereafter be, in any manner entitled at law or in equity.

     TO HAVE AND TO HOLD all said properties, real, personal and mixed,
mortgaged, pledged and conveyed by the Company as aforesaid, or intended so to
be, unto the Trustee and its successors and assigns forever;

     SUBJECT, HOWEVER, to the exceptions and reservations and matters
hereinabove recited, to existing leases, to existing liens upon rights of way
for transmission or distribution line purposes, as defined in Article I of the
Original Indenture, and any extensions thereof, and subject to existing
easements for streets, alleys, highways, rights-of-way and railroad purposes
over, upon and across certain of the property hereinbefore described, and
subject also to all the terms, conditions, agreements, covenants, exceptions and
reservations expressed or provided in the deeds or other instruments
respectively under and by virtue of which the Company acquired the properties
hereinabove described, and to undetermined liens and charges, if any, incidental
to construction or other existing permitted liens as defined in Article I of the
Original Indenture;

     IN TRUST, NEVERTHELESS, upon the terms and trusts in the Original Indenture
and the indentures supplemental thereto, including this Supplemental Indenture,
set forth, for the equal and proportionate benefit and security of all present
and future holders of the Bonds and coupons issued and to be issued thereunder,
or any of them, without preference of any of said Bonds and coupons of any
particular series over the Bonds and coupons of any other series, by reason of
priority in the time of the issue, sale or negotiation thereof, or by reason of
the purpose of issue or otherwise howsoever, except as otherwise provided in
Section 2 of Article IV of the Original Indenture.

     AND IT IS HEREBY COVENANTED, DECLARED AND AGREED, by and between the
parties hereto, for the benefit of those who shall hold the Bonds and coupons,
or any of them to be issued under the Original Indenture, as follows:

                                       10
<Page>

                                    ARTICLE I

                          DESCRIPTION OF THE NEW BONDS

     Section 1. There is hereby created a new series of Bonds to be executed,
authenticated and delivered under and secured by the Original Indenture which
shall, subject to the provisions of Section 1 of Article II of the Original
Indenture, be designated as "First Mortgage Bonds, Senior Notes Series AA" (the
"New Bonds") of the Company. The New Bonds shall be executed, authenticated and
delivered in accordance with the provisions of, and shall in all respects be
subject to all of the terms, conditions and covenants of, the Original Indenture
and shall be issued to, and registered in the name of, the Senior Note Trustee
under the Senior Note Indenture to secure any and all obligations of the Company
under the Senior Notes and any other series of senior notes from time to time
outstanding under the Senior Note Indenture.

     The New Bonds shall mature on September 1, 2012, and shall bear interest at
the rate per annum set forth in the form of the New Bond contained in Section 3
of this Article I, payable semi-annually on the 1st day of March and the 1st day
of September in each year, commencing on March 1, 2003, and at maturity. The New
Bonds shall be payable as to principal, premium, if any, and interest in any
coin or currency of the United States of America which at the time of payment is
legal tender for public and private debts, and shall be payable, in immediately
available funds, at the office of the Senior Note Trustee.

     Section 2. The New Bonds shall not be assignable or transferable except as
permitted or required by Section 4.04 of the Senior Note Indenture. Any such
transfer shall be effected at the principal office or place of business of the
Trustee under the Original Indenture. The New Bonds are exchangeable for the New
Bonds of other denominations, as in the Original Indenture provided, except that
payment of a service charge therefor will not be required by the Company.

     Notwithstanding the provisions of Section 6 of Article II of the Original
Indenture, the New Bonds shall be dated the date of authentication and shall
bear interest from the interest payment date to which interest on the New Bonds
has been paid next preceding the date thereof, unless such date is an interest
payment date to which interest has been paid, in which case they shall bear
interest from the date thereof, or unless the date thereof is prior to March 1,
2003, in which case they shall bear interest from August 22, 2002; provided,
however, that, subject to the provisions of this Section with respect to failure
by the Company to pay any interest on an interest payment date, the holder of
any New Bond dated after a record date (as hereinafter defined) for the payment
of interest and prior to the date of payment of such interest shall not be
entitled to payment of such interest and shall have no claim against the Company
with respect thereto.

     The person in whose name any New Bond is registered at the close of
business on any record date with respect to any interest payment date shall be
entitled to receive the interest payable on such interest payment date
notwithstanding the cancellation of such Bond upon any transfer or exchange
thereof subsequent to the record date and prior to such interest payment date,
except if and to the extent the Company shall default in the payment of the
interest due on such interest payment date, in which case such defaulted
interest shall be paid to the person in whose name such Bond is registered on
the date of payment of such defaulted interest or on a subsequent record date
for such payment if one shall have been established as hereinafter

                                       11
<Page>

provided. A subsequent record date may be established by the Company by notice
mailed to the holders of the New Bonds not less than ten days preceding such
record date, which record date shall be not more than thirty days prior to the
subsequent interest payment date. The term "record date" as used in this Section
with respect to any regular interest payment date shall mean the February 15 or
August 15, as the case may be, next preceding such interest payment date, or, if
such February 15 or August 15 shall be a legal holiday in the State of New York
or in the State of Missouri or a day on which banking institutions in the
Borough of Manhattan, The City of New York, or the City of St. Louis, Missouri,
are authorized by law to close, the next preceding day which shall not be a
legal holiday or a day on which such institutions are so authorized to close.

     Upon any payment of the principal of, premium, if any, and interest on, all
or any portion of the Senior Notes, whether at maturity or prior to maturity by
redemption or otherwise or upon provision for the payment thereof having been
made in accordance with Section 5.01(a) of the Senior Note Indenture, the New
Bonds in a principal amount equal to the principal amount of such Senior Notes
and having both a corresponding maturity date and interest rate shall, to the
extent of such payment of principal, premium, if any, and interest, be deemed
paid and the obligation of the Company thereunder to make such payment shall be
discharged to such extent and, in the case of the payment of principal (and
premium, if any), such New Bonds shall be surrendered to the Company for
cancellation as provided in Section 4.08 of the Senior Note Indenture. The
Trustee may at any time and all times conclusively assume that the obligation of
the Company to make payments with respect to the principal of and premium, if
any, and interest on the Senior Notes, so far as such payments at the time have
become due, has been fully satisfied and discharged pursuant to the foregoing
sentence unless and until the Trustee shall have received a written notice from
the Senior Note Trustee signed by one of its officers stating (i) the timely
payment of principal, or premium, if any, or interest on, the Senior Notes has
not been made, (ii) that the Company is in arrears as to the payments required
to be made by it to the Senior Note Trustee pursuant to the Senior Note
Indenture, and (iii) the amount of the arrearage.

     Section 3. The New Bonds and the Trustee's certificate on the New Bonds
shall be substantially in the following forms respectively:

                                       12
<Page>

                           [FORM OF FACE OF NEW BOND]

No.____                                                                $________
                               III. C. C. No. 6226

            NOTWITHSTANDING ANY PROVISIONS HEREOF OR IN THE ORIGINAL
         INDENTURE THIS BOND IS NOT ASSIGNABLE OR TRANSFERABLE EXCEPT AS
         PERMITTED OR REQUIRED BY SECTION 4.04 OF THE INDENTURE DATED AS
         OF AUGUST 15, 2002, BETWEEN UNION ELECTRIC COMPANY AND THE BANK
                            OF NEW YORK, AS TRUSTEE.

                             UNION ELECTRIC COMPANY
             (Incorporated under the laws of the State of Missouri)
                  First Mortgage Bonds, Senior Notes Series AA

     UNION ELECTRIC COMPANY, a corporation organized and existing under the laws
of the State of Missouri (hereinafter called the "Company", which term shall
include any successor corporation as defined in the Amended Indenture referred
to on the reverse hereof), for value received, hereby promises to pay to The
Bank of New York, as trustee under the Senior Note Indenture hereinafter
referred to, or registered assigns, the sum of _________________________________
Dollars, on the 1st day of September, 2012 in any coin or currency of the United
States of America which at the time of payment is legal tender for public and
private debts, and to pay interest thereon, in like coin or currency, at the
rate of FIVE AND ONE QUARTER per centum (5.25%) per annum, payable
semi-annually, on March 1 and September 1 in each year until maturity,
commencing March 1, 2003, and at maturity or, if the Company shall default in
the payment of the principal hereof, until the Company's obligation with respect
to the payment of such principal shall be discharged as provided in the Amended
Indenture referred to on the reverse hereof. Such interest shall be payable from
the March 1 or September 1, as the case may be, next preceding the date hereof
to which interest has not been paid, unless the date hereof is a March 1 or
September 1 to which interest has been paid, in which case from the date hereof,
or unless the date hereof is prior to the first payment of interest, in which
case from August 22, 2002. The interest so payable will be paid to the person in
whose name this Bond, or the Bond in exchange or substitution for which this
Bond shall have been issued, shall have been registered at the close of business
on the February 15 or August 15, as the case may be, next preceding the date of
payment, subject to certain exceptions set forth in the Amended Indenture. The
principal of, and interest and premium, if any, on, this Bond are payable, in
immediately available funds, at the office of the Senior Note Trustee
hereinafter referred to.

     Under an Indenture dated as of August 15, 2002 (the "Senior Note
Indenture") between the Company and The Bank of New York, as trustee (the
"Senior Note Trustee"), the Company will issue, concurrently with the issuance
of this Bond, an issue of notes under the Senior Note Indenture entitled "5.25%
Senior Secured Notes due 2012" (the "Senior Notes"). Pursuant to Article IV of
the Senior Note Indenture, this Bond is issued to the Senior Note Trustee to
secure any and all obligations of the Company under the Senior Notes and any
other series of senior notes from time to time outstanding under the Senior Note
Indenture. Payment of principal of, or premium, if any, or interest on, the
Senior Notes shall constitute payments on this Bond as

                                       13
<Page>

further provided herein and in the Supplemental Indenture dated August 15, 2002
pursuant to which this Bond has been issued (the "Supplemental Indenture").

     Upon any payment of the principal of, premium, if any, and interest on, all
or any portion of the Senior Notes, whether at maturity or prior to maturity by
redemption or otherwise or upon provision for the payment thereof having been
made in accordance with Section 5.01(a) of the Senior Note Indenture, a
principal amount of this Bond equal to the principal amount of such Senior Notes
and having both a corresponding maturity date and interest rate shall, to the
extent of such payment of principal, premium, if any, and interest, be deemed
paid and the obligation of the Company thereunder to make such payment shall be
discharged to such extent and, in the case of the payment of principal (and
premium, if any), such bonds shall be surrendered to the Company for
cancellation as provided in Section 4.08 of the Senior Note Indenture. The
Trustee (as hereinafter defined) may at anytime and all times conclusively
assume that the obligation of the Company to make payments with respect to the
principal of and premium, if any, and interest on, the Senior Notes, so far as
such payments at the time have become due, has been fully satisfied and
discharged pursuant to the foregoing sentence unless and until the Trustee shall
have received a written notice from the Senior Note Trustee signed by one of its
officers stating (i) that timely payment of principal, or premium or interest
on, the Senior Notes has not been made, (ii) that the Company is in arrears as
to the payments required to be made by it to the Senior Note Trustee pursuant to
the Senior Note Indenture, and (iii) the amount of the arrearage.

     For purposes of Section 4.09 of the Senior Note Indenture, this Bond shall
be deemed to be the "Related Series of Senior Note First Mortgage Bonds" in
respect of the Senior Notes.

     This Bond shall not be entitled to any benefit under the Amended Indenture
or any indenture supplemental thereto, or become valid or obligatory for any
purpose, until The Bank of New York, the Trustee under the Amended Indenture, or
a successor trustee thereto under the Amended Indenture, or an agent therefor,
shall have signed the form of certificate endorsed hereon.

     The provisions of this Bond are continued on the reverse hereof and such
continued provisions shall for all purposes have the same effect as though fully
set forth at this place.

     IN WITNESS WHEREOF, Union Electric Company has caused this Bond to be
signed in its name by its Chairman of the Board or President or a Vice President
by manual signature or a facsimile thereof, and its corporate seal (or a
facsimile thereof) to be hereto affixed and attested by its Secretary or an
Assistant Secretary by manual signature or a facsimile thereof.

     Dated,

                                         UNION ELECTRIC COMPANY,


                                         By
                                           ------------------------
                                               Vice President

[CORPORATE SEAL]

Attest:
- ------------------------------------
Secretary

                                       14
<Page>

                         [FORM OF TRUSTEE'S CERTIFICATE]

     This Bond is one of the Bonds, of the series designated therein, described
in the within-mentioned Amended Indenture and Supplemental Indenture of August
15, 2002.


                                         THE BANK OF NEW YORK, as
                                         TRUSTEE


                                         By
                                           ------------------------------
                                               Authorized Officer

                          [FORM OF REVERSE OF NEW BOND]

     This Bond is one of a duly authorized issue of Bonds of the Company (herein
called the "Bonds"), in unlimited aggregate principal amount, of the series
hereinafter specified, all issued and to be issued under and equally secured by
the indenture of mortgage and deed of trust, dated June 15, 1937, executed by
the Company to The Bank of New York (successor trustee to Bank of America,
National Association, formerly Boatmen's Trust Company), as trustee (herein
called the "Trustee"), as amended by indentures supplemental thereto dated May
1, 1941, April 1, 1971, February 1, 1974, July 7, 1980 and February 1, 2000,
between the Company and the Trustee (said mortgage and deed of trust, as so
amended, being herein called the "Amended Indenture"), to which Amended
Indenture and all indentures supplemental thereto reference is hereby made for a
description of the properties mortgaged and pledged, the nature and extent of
the security, the rights of the bearers or registered owners of the Bonds and of
the Trustee in respect thereto, and the terms and conditions upon which the
Bonds are, and are to be, secured. To the extent permitted by, and as provided
in, the Amended Indenture, modifications or alterations of the Amended
Indenture, or of any indenture supplemental thereto, and of the rights and
obligations of the Company and of the holders of the Bonds may be made with the
consent of the Company by an affirmative vote of not less than 60% in amount of
the Bonds entitled to vote then outstanding, at a meeting of Bondholders called
and held as provided in the Amended Indenture, and by an affirmative vote of not
less than 60% in amount of the Bonds of any series entitled to vote then
outstanding and affected by such modification or alteration, in case one or more
but less than all of the series of Bonds then outstanding under the Amended
Indenture are so affected. Additionally, the Company may amend the Amended
Indenture, as supplemented, by an appropriate written consent of not less than
60% in aggregate principal amount of the Bonds outstanding without a meeting of
such Bondholders. No such modification or alteration shall be made which will
affect the terms of payment of the principal of, or interest or premium on, this
Bond, which are unconditional. The Bonds may be issued in series, for various
principal sums, may mature at different times, may bear interest at different
rates and may otherwise vary as in the Amended Indenture provided. This Bond is
one of a series designated as the "First Mortgage Bonds, Senior Notes Series AA"
(herein called the "Bonds of this Series") of the Company, issued under and
secured by the Amended Indenture and described in the indenture (hereinafter
called the "New Supplemental Indenture") dated August 15, 2002, between the
Company and the Trustee, supplemental to the Amended Indenture.

     The Bonds of this Series are not entitled to the benefit of any
improvement, maintenance or analogous fund.

                                       15
<Page>

     This Bond is not redeemable except on the date, in the principal amount and
for the redemption price that correspond to the redemption dates for, the
principal amount to be redeemed of, and the redemption price for, the Senior
Notes, and except upon written demand of the Senior Note Trustee following the
occurrence of an event of default under the Senior Note Indenture and the
acceleration of the Senior Notes, as provided in Section 8.01 of the Senior Note
Indenture.

     In case an event of default, as defined in the Amended Indenture, shall
occur, the principal of all the Bonds at any such time outstanding under the
Amended Indenture may be declared or may become due and payable, upon the
conditions and in the manner and with the effect provided in the Amended
Indenture. The Amended Indenture provides that such declaration may in certain
events be waived by the holders of a majority in principal amount of the Bonds
outstanding.

     This Bond shall not be assignable or transferable except as permitted or
required by Section 4.04 of the Senior Note Indenture. This Bond is exchangeable
by the registered owner hereof, in person or by duly authorized attorney, on the
books of the Company to be kept for that purpose at the office of the Company in
the City of St. Louis, Missouri, upon surrender and cancellation of this Bond
and on presentation of a duly executed written instrument of transfer, and
thereupon a new Bond or Bonds of the same series, of the same aggregate
principal amount and in authorized denominations will be issued to the
transferee or transferees in exchange herefor, without payment of any charge
other than stamp taxes and other governmental charges incident thereto; and this
Bond with or without others of like series, may in like manner be exchanged for
one or more new Bonds of the same series of other authorized denominations but
of the same aggregate principal amount; all subject to the terms and conditions
set forth in the Amended Indenture.

     As provided in Section 4.11 of the Senior Note Indenture, from and after
the Release Date (as defined in the Senior Note Indenture), the obligations of
the Company with respect to this Bond shall be deemed to be satisfied and
discharged, this Bond shall cease to secure in any manner any Senior Notes
outstanding under the Senior Note Indenture, and, pursuant to Section 4.08 of
the Senior Note Indenture, the Senior Note Trustee shall forthwith deliver this
Bond to the Company for cancellation.

     No recourse shall be had for the payment of the principal of, premium, if
any, on or the interest on, this Bond, or for any claim based hereon or on the
Amended Indenture or any indenture supplemental thereto, against any
incorporator, or against any stockholder, director or officer, past, present or
future, of the Company, or of any predecessor or successor corporation, either
directly or through the Company or any such predecessor or successor
corporation, whether for amounts unpaid on stock subscriptions or by virtue of
any constitution, statute or rule of law, or by the enforcement of any
assessment or penalty or otherwise, all such liability, whether at common law,
in equity, by any constitution, statute or otherwise, of incorporators,
stockholders, directors or officers being released by every owner hereof by the
acceptance of this Bond and as part of the consideration for the issue hereof,
and being likewise released by the terms of the Amended Indenture.

                      [END OF FORM OF REVERSE OF NEW BOND]

     Section 4. Until New Bonds in definitive form are ready for delivery, the
Company may execute, and upon its request in writing the Trustee shall
authenticate and deliver, in lieu

                                       16
<Page>

thereof, New Bonds in temporary form, as provided in Section 9 of Article II of
the Original Indenture.

                                   ARTICLE II

                             ISSUE OF THE NEW BONDS

     Section 1. The principal amount of the New Bonds which may be authenticated
and delivered hereunder is limited to an amount equal to the principal amount of
the Senior Notes issued under the Senior Note Indenture and secured thereby and
are further subject to the limitations regarding the principal amount of Bonds
which may be issued under the Original Indenture set forth therein.

     Section 2. The New Bonds in the aggregate principal amount of One Hundred
Seventy Three Million Dollars ($173,000,000), being the initial issue of the New
Bonds, may forthwith at any time or from time to time be executed by the Company
and delivered to the Trustee and shall be authenticated by the Trustee and
delivered (either before or after the filing or recording hereof) to or upon the
order of the Company, upon compliance by the Company with the applicable
provisions of Article III and Article XVIII of the Original Indenture.

     Section 3. For purposes of Section 4.09 of the Senior Note Indenture, the
New Bonds shall be deemed to be the "Related Series of Senior Notes First
Mortgage Bonds" in respect of the Senior Notes.

     Section 4. As provided in Section 4.11 of the Senior Note Indenture, from
and after the Release Date (as defined in the Senior Note Indenture), the
obligations of the Company with respect to the New Bonds shall be deemed to be
satisfied and discharged, the New Bonds shall cease to secure in any manner any
Notes outstanding under the Senior Note Indenture, and, pursuant to Section 4.08
of the Senior Note Indenture, the Senior Note Trustee shall forthwith deliver
the New Bonds to the Company for cancellation.

                                   ARTICLE III

                           REDEMPTION OF THE NEW BONDS

     Section 1. The New Bonds are not redeemable except on the date, in the
principal amount and for the redemption price that correspond to the redemption
date for, the principal amount to be redeemed of, and the redemption price for,
the Senior Notes, and except as set forth in Section 2 of this Article III.

     In the event that the Company redeems any Senior Notes prior to maturity in
accordance with the provisions of the Senior Note Indenture, the Senior Note
Trustee shall on the same date deliver to the Company the New Bonds in principal
amount corresponding to the Senior Notes so redeemed, as provided in Section
4.08 of the Senior Note Indenture. The Company agrees to give the Senior Note
Trustee notice of any such redemption of the Senior Notes on or before the date
fixed for any such redemption.

     There shall be no improvement, maintenance or analogous fund for the New
Bonds.

                                       17
<Page>

     Section 2. Upon the occurrence of an Event of Default under the Senior Note
Indenture and the acceleration of the Senior Notes, the New Bonds shall be
redeemable in whole upon receipt by the Trustee of a written demand (hereinafter
called a "Redemption Demand") from the Senior Note Trustee stating that there
has occurred under the Senior Note Indenture both an Event of Default and a
declaration of acceleration of payment of principal, accrued interest and
premium, if any, on the Senior Notes specifying the last date to which interest
on such Senior Notes has been paid (such date being hereinafter referred to as
the "Initial Interest Accrual Date") and demanding redemption of the New Bonds.
The Company waives any right it may have to prior notice of such redemption
under the Original Indenture. Upon surrender of the New Bonds by the Senior Note
Trustee to the Trustee, the New Bonds shall be redeemed at a redemption price
equal to the principal amount thereof plus accrued interest thereon from the
Initial Interest Accrual Date to the date of the Redemption Demand; provided,
however, that in the event of a rescission or annulment of acceleration of the
Senior Notes pursuant to the last paragraph of Section 8.01(a) of the Senior
Note Indenture, then any Redemption Demand shall thereby deemed to be rescinded
by the Senior Note Trustee although no such rescission or annulment shall extend
to or affect any subsequent default or impair any right consequent thereon.

                                   ARTICLE IV

                                    COVENANTS

     The Company hereby covenants, warrants and agrees;

     Section 1. That the Company is lawfully seized and possessed of all of the
mortgaged property described in the granting clauses of this Supplemental
Indenture; that it has good right and lawful authority to mortgage the same as
provided in this Supplemental Indenture; and that such mortgaged property is, at
the actual date of the issue of the New Bonds, free and clear of any deed of
trust, mortgage, lien, charge or encumbrance thereon or affecting the title
thereto prior to the Original Indenture, except as set forth in the granting
clauses of the Original Indenture or this Supplemental Indenture.

     Section 2. That, so long as any of the New Bonds are outstanding, whenever
any officers' certificate is required to be filed or deposited with the Trustee
pursuant to Section 3(b) of Article III of the Original Indenture upon an
application for the authentication of additional Bonds pursuant to Article III
of the Original Indenture, such officers' certificate shall include, in addition
to the matters required to be stated therein by said Section 3(b), the statement
with respect to the net earnings of the Company available for interest after
property retirement appropriations required by Section 2 of Article V of the
Supplemental Indenture of July 1, 1956.

     Section 3. That, so long as any of the New Bonds are outstanding, the
Company will not apply for the authentication and delivery of additional Bonds
pursuant to Section 4 of Article III of the Original Indenture or the withdrawal
of cash from the trust estate or the reduction of the amount of cash required to
be paid into the trust estate or to satisfy the maintenance and improvement
funds under any provision of the Original Indenture or the Supplemental
Indentures creating prior series of Bonds, on the basis of the amount of
$15,000,000 excluded from net bondable value of property additions not subject
to an unfunded prior lien pursuant to Section 3 of Article V of the Supplemental
Indenture of October 1, 1945, or on the basis of the amount of $7,500,000
excluded from net bondable value of property additions not subject to an

                                       18
<Page>

unfunded prior lien pursuant to Section 3 of Article V of the Supplemental
Indenture of July 1, 1956.

     Section 4. That, so long as any of the New Bonds are outstanding, the
Company will not issue or permit to be issued any prior lien bonds secured by an
unfunded prior lien in addition to the prior lien bonds secured by such unfunded
prior lien at the time of first acquisition by the Company of property subject
thereto (other than in lieu of lost, stolen or mutilated bonds or on the
exchange for bonds already outstanding of an equal principal amount of other
bonds of the same issue and the same series, if any, and of the same maturity),
except upon compliance with the provisions of Section 16 of Article IV of the
Original Indenture, nor unless the net earnings of the Company available for
interest after property retirement appropriations (determined as provided in
Section 2 of Article V of the Supplemental Indenture of July 1, 1956), for any
twelve consecutive calendar months during the period of fifteen calendar months
immediately preceding the first day of the month in which the additional prior
lien bonds are to be issued, have been, in the aggregate, equal to not less than
twice the annual interest charges on the indebtedness specified in subparagraphs
(i) and (ii) of paragraph (1) of Section 2(a) of said Article V; provided that,
if the application for the issue of such additional prior lien bonds is upon the
basis of payment at maturity of prior lien bonds theretofore sold or otherwise
disposed of or the redemption or purchase thereof after a date two years prior
to the date of maturity, the additional requirement imposed by this Section 4
with respect to net earnings of the Company available for interest after
property retirement appropriations shall not apply. Any officers' certificate
with respect to net earnings of the Company, required to be filed with the
Trustee as a condition precedent to the issue of such additional prior lien
bonds, shall include, in addition to the matters otherwise required to be stated
therein, the matters required to be stated in an officers' certificate pursuant
to paragraphs (1) and (2) of Section 2(a) of said Article V.

     Section 5. That, so long as any of the New Bonds are outstanding, the
Company will not acquire, by purchase, merger or otherwise, any property subject
to a lien or liens which will on acquisition be an unfunded prior lien or prior
liens, except upon compliance with the provisions of Section 14 of Article IV of
the Original Indenture, nor unless the net earnings of such property available
for interest after property retirement appropriations (determined in the manner
provided in Section 2 of Article V of the Supplemental Indenture of July 1,
1956), for any twelve consecutive calendar months during the period of fifteen
calendar months immediately preceding the first day of the month in which the
first acquisition of property subject to such lien or liens occurs, have been,
in the aggregate, equal to not less than twice the amount of annual interest
charges, on all outstanding indebtedness secured by such lien or liens. Any
officers' certificate with respect to net earnings of such property, required to
be filed with the Trustee as a condition precedent to the acquisition of such
property, shall include, in addition to the matters otherwise required to be
stated therein, the matters required to be stated in an officers' certificate
pursuant to Section 2 of said Article V applicable, however, only to the net
earnings of such property and to the indebtedness secured by such liens to which
such property is subject.

                                       19
<Page>

                                    ARTICLE V

                                   THE TRUSTEE

     The Trustee hereby accepts the trusts hereby declared and provided, and
agrees to perform the same upon the terms and conditions in the Original
Indenture and in this Supplemental Indenture set forth, and upon the following
terms and conditions:

     The Trustee shall not be responsible in any manner whatsoever for or in
respect of the validity or sufficiency of this Supplemental Indenture or the due
execution hereof by the Company or for or in respect of the recitals contained
herein, all of which recitals are made by the Company solely.

                                   ARTICLE VI

           AMENDMENTS OF CERTAIN PROVISIONS OF THE ORIGINAL INDENTURE.

     Section 1. Pursuant to the reservation of right in the Supplemental
Indenture of August 16, 1976 and each supplemental indenture dated thereafter,
and there being no outstanding Bonds of any series created prior to the Bonds
created by such Supplemental Indenture of August 16, 1976, the Company hereby
amends the Original Indenture, as supplemented, so as to substitute in Article
XV thereof "sixty percent (60%)" for "eighty percent (80%)" wherever appearing
in said Article XV.

     Section 2. Pursuant to the reservation of right in the Supplemental
Indenture of August 16, 1976 and each supplemental indenture dated thereafter,
and there being no outstanding Bonds of any series created prior to the Bonds
created by such Supplemental Indenture of August 16, 1976, the Company hereby
amends the Original Indenture, as supplemented, to amend Article XV thereof by
adding thereto a Section 9 to read as follows:

          "SECTION 9. (A) Anything in this Article XV contained to the contrary
          notwithstanding, the Trustee shall receive the written consent (in any
          number of instruments of similar tenor executed by Bondholders or by
          their attorneys appointed in writing) of the holders of sixty percent
          (60%) or more in principal amount of the Bonds outstanding hereunder,
          and, if the rights of one or more, but less than all, series of Bonds
          then outstanding are to be affected by action taken pursuant to such
          consent, then also by consent of the holders of at least sixty percent
          (60%) in principal amount of each series of Bonds so to be affected
          and outstanding hereunder (at the time the last such needed consent is
          delivered to the Trustee) in lieu of the holding of a meeting pursuant
          to this Article XV and in lieu of all action at such a meeting and
          with the same force and effect as a resolution duly adopted in
          accordance with the provisions of Section 6 of this Article XV.

               (B) Instruments of consent shall be witnessed or in the
          alternative may (a) have the signature guaranteed by a bank or trust
          company or a registered dealer in securities, (b) be acknowledged
          before a Notary Public or other officer authorized to take
          acknowledgements, or (c)

                                       20
<Page>

          have their genuineness otherwise established to the satisfaction of
          the Trustee.

               The amount of Bonds payable to bearer, and the series and serial
          numbers thereof, held by a person executing an instrument of consent
          (or whose attorney has executed an instrument of consent in his
          behalf), and the date of his holding the same may be proved by
          exhibiting the Bonds to and obtaining a certificate executed by (i)
          any bank or trust or insurance company, or (ii) any trustee,
          secretary, administrator or other proper officer of any pension,
          welfare, hospitalization or similar fund or funds, or (iii) the United
          States of America, any Territory thereof, the District of Columbia,
          any State of the United States or any public instrumentality of the
          United States, or of any State or of any Territory, or (iv) any other
          person or corporation satisfactory to the Trustee. A Bondholder in any
          of the foregoing categories may sign a certificate in his own behalf.

               Each such certificate shall be dated and shall state, in effect,
          that as of the date thereof, a coupon Bond or Bonds bearing a
          specified serial number or numbers was deposited with or exhibited to
          the signer of such certificate. The holding by the person named in any
          such certificate of any Bond specified therein shall be presumed to
          continue unless (1) any certificate bearing a later date issued in
          respect of the same Bond shall be produced, (2) the Bond specified in
          such certificate (or any Bond or Bonds issued in exchange or
          substitution for such Bond) shall be produced by another holder, or
          (3) the Bond specified in such certificate shall be registered as to
          principal in the name of another holder or shall have been surrendered
          in exchange for a fully registered bond registered in the name of
          another holder. The Trustee may nevertheless, in his discretion,
          require further proof in cases where it deems further proof desirable.
          The ownership of registered Bonds shall be proved by the registry
          books.

               (C) Until such time as the Trustee shall receive the written
          consent of the necessary per cent. in principal amount of the Bonds
          required by the provisions of subsection (A) above for action
          contemplated by such consent, any holder of a Bond, the serial number
          of which is shown by the evidence to be included in the Bonds the
          holders of which have consented to such action, may, by filing written
          notice with the Trustee at its principal office and upon proof of
          holding as provided in subsection (B) above, revoke such consent so
          far as it concerns such Bond. Except as aforesaid, any such action
          taken by the holder of any Bond shall be conclusive and binding upon
          such holder and upon all future holders of such Bond (and any Bond
          issued in lieu thereof or exchanged therefor), irrespective of whether
          or not any notation of such consent is made upon such Bond, and in any
          event any action taken by the holders of the percentage in aggregate
          principal amount of the Bonds specified in subsection (A) above in
          connection with such action shall be conclusively binding upon the
          Company, the Trustee and the holders of all the Bonds."

                                       21
<Page>

                                   ARTICLE VII

                            MISCELLANEOUS PROVISIONS.

     Section 1. Except as otherwise defined herein, all terms contained in this
Supplemental Indenture shall, for all purposes thereof, have the meanings given
to such terms in Article I of the Original Indenture.

     Section 2. This Supplemental Indenture may be simultaneously executed in
any number of counterparts, each of which when so executed shall be deemed to be
an original; but such counterparts shall together constitute but one and the
same instrument.

                                       22
<Page>

     IN WITNESS WHEREOF, said Union Electric Company has caused this
Supplemental Indenture to be executed on its behalf by its Chairman of the Board
or President or one of its Vice Presidents and its corporate seal to be hereto
affixed and said seal and this Supplemental Indenture to be attested by its
Secretary or one of its Assistant Secretaries; and said The Bank of New York, in
evidence of its acceptance of the trust hereby created, has caused this
Supplemental Indenture to be executed on its behalf by its President or one of
its Vice Presidents, and its corporate seal to be hereto affixed and said seal
and this Supplemental Indenture to be attested by its Secretary, or one of its
Assistant Secretaries; all as of the 15th day of August, Two thousand and two.


Attested:                               UNION ELECTRIC COMPANY,
                                           1901 Chouteau Avenue
                                           St. Louis, Missouri 63103

       /s/ G. L. Waters                 By:       /s/ Warner L. Baxter
- ----------------------------------         -----------------------------
     G. L. Waters                       Name:  Warner L. Baxter
     Assistant Secretary                Title: Senior Vice President


Signed, sealed and delivered by
   UNION ELECTRIC COMPANY
   in the presence of:

       /s/ Daphyne H. Bradley
- ----------------------------------
     Daphyne H. Bradley

       /s/ D. T. McGillicuddy
- ----------------------------------
     D. T. McGillicuddy
            As Witnesses


Attested:                               THE BANK OF NEW YORK,
                                           911 Washington Avenue
                                           St. Louis, Missouri 63101


       /s/ Linda Krull                  By:    /s/ J. Bruce Herd
- ----------------------------------         -------------------------------------
    Linda Krull                         Name:  J. Bruce Herd
    As Agent for The Bank of New York   Title: As Agent for the Bank of New York


Signed, sealed and delivered by
    THE BANK OF NEW YORK
    in the presence of:

       /s/ P. C. QuiBelle
- ----------------------------------
    P. C. QuiBelle

       /s/ N. Mogelnicki
- ----------------------------------
    N. Moglenicki
            As Witnesses

                                       23
<Page>

STATE OF MISSOURI,         }
                           } SS.:
CITY OF ST. LOUIS,         }

     On this 19th day of August 2002, before me appeared WARNER L. BAXTER, to me
personally known, who, being by me duly sworn, did say that he is a Senior Vice
President of THE BANK OF NEW YORK, a corporation, and that the seal affixed to
the foregoing instrument is the corporate seal of said corporation, and that
said instrument was signed and sealed in behalf of said corporation, as the
trustee thereunder by authority of its Board of Directors, and said WARNER L.
BAXTER, acknowledged said instrument to be the free act and deed of said
corporation as the trustee under said instrument.

     IN TESTIMONY WHEREOF, I have hereto set my hand and affixed my official
seal at my office, in the City and State aforesaid, the day and year last above
written.


                                           /s/ Mary Hoyt
                                      ------------------------------------------
                                           Mary Hoyt

                                      MARY HOYT
                                      NOTARY PUBLIC - NOTARY SEAL
                                      STATE OF MISSOURI
                                      JEFFERSON COUNTY
                                      MY COMMISSION EXPIRES APRIL 1, 2006

                                       24
<Page>

STATE OF MISSOURI,         }
                           } SS.:
CITY OF ST. LOUIS,         }

     On this 19th day of August 2002, before me appeared WARNER L. BAXTER, to me
personally known, who, being by me duly sworn, did say that he is a Senior Vice
President of THE BANK OF NEW YORK, a corporation, and that the seal affixed to
the foregoing instrument is the corporate seal of said corporation, and that
said instrument was signed and sealed in behalf of said corporation, as the
trustee thereunder by authority of its Board of Directors, and said WARNER L.
BAXTER, acknowledged said instrument to be the free act and deed of said
corporation as the trustee under said instrument.

     IN TESTIMONY WHEREOF, I have hereto set my hand and affixed my official
seal at my office, in the City and State aforesaid, the day and year last above
written.


                                           /s/ Mary Hoyt
                                      ------------------------------------------
                                           Mary Hoyt

                                      MARY HOYT
                                      NOTARY PUBLIC - NOTARY SEAL
                                      STATE OF MISSOURI
                                      JEFFERSON COUNTY
                                      MY COMMISSION EXPIRES APRIL 1, 2006

                                       25