Document:

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                                                                     Exhibit 4.4

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 MARCH 5, 2003

                             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 BB

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

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       SUPPLEMENTAL INDENTURE, dated the 5th day of March, Two thousand and
three (2003) 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, February 1, 2000 and
August 15, 2002 (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, February 1, 2000 and
August 15, 2002, 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

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       described in the Supplemental Indenture dated October 1, 1945
       (hereinafter called the "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;

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              (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 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

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       Indenture of April 1, 1971"), all of which have been redeemed prior to
       the date of the execution hereof;

              (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;

                                       4
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              (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 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 have been redeemed prior to 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 have been paid at maturity prior to 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

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       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 $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;

              (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

              (45) $173,000,000 principal amount of First Mortgage Bonds, Senior
       Notes Series AA (herein called the "Bonds of 2012 Series"), which are
       described in the

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       Supplemental Indenture dated August 15, 2002 (hereinafter called the
       "Supplemental Indenture of August 15, 2002"), 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
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 $184,000,000
aggregate principal amount of the Company's 5.50% Senior Secured Notes due 2034
(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

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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 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

       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, August 15, 2002 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.

                                       9
<Page>

                                     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 BB" (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 March 15, 2034, 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 15th day of March and the 15th
day of September in each year, commencing on September 15, 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 September
15, 2003, in which case they shall bear interest from March 10, 2003; 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 March 1 or
September 1, as the case may be, next preceding such interest payment date, or,
if such March 1 or September 1 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
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:

                           [FORM OF FACE OF NEW BOND]

No. ____                                                               $________

                               Ill. C. C. No. 6247

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 BB

       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

                                       12
<Page>

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 15th day of March, 2034 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 HALF per centum
(5.50%) per annum, payable semi-annually, on March 15 and September 15 in each
year until maturity, commencing September 15, 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 15 or September 15, as the
case may be, next preceding the date hereof to which interest has not been paid,
unless the date hereof is a March 15 or September 15 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 March 10, 2003. 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 March 1 or September 1, 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 "5.50%
Senior Secured Notes due 2034" (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 further provided herein
and in the Supplemental Indenture dated March 5, 2003 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
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 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) 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.

                                       13
<Page>

       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

                         [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 March 5, 2003.

                                             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

                                       14
<Page>

1, 1971, February 1, 1974, July 7, 1980, February 1, 2000 and August 15, 2002,
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 (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 60% in principal amount of each series of Bonds so to be
affected and outstanding hereunder) 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 BB" (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 March 5, 2003, 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.

       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

                                       15
<Page>

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 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
Eighty Four Million Dollars ($184,000,000), 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

                                       16
<Page>

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
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 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.

       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 be 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.

                                       17
<Page>

                                   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
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

                                       18
<Page>

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.

                                    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

                            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.

                                       19
<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 5th day of March, Two thousand and three.

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

     /s/ G. L. Waters                     By:    /s/ Jerre E. Birdsong
     -------------------------------          ----------------------------------
     G. L. Waters                         Name:  Jerre E. Birdsong
     Assistant Secretary                  Title: Vice President and Treasurer

Signed, sealed and delivered by

     UNION ELECTRIC COMPANY
     in the presence of:

     /s/ Daphyne Bradley
     -------------------------------
      Daphyne Bradley

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

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

     /s/ Daniel G. Dwyer                  By: /s/ Belinda Brown
     -------------------------------          ----------------------------------
     Daniel G. Dwyer                      Name:  Belinda Brown
     Vice President                       Title:  Vice President
                                                  As Agent

Signed, sealed and delivered by

     THE BANK OF NEW YORK
     in the presence of:

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

     /s/ Richard F. Novosak
     -------------------------------
       Richard F. Novosak
              As Witnesses

                                       20
<Page>

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

       On this 5th day of March 2003, before me appeared JERRE E. BIRDSONG, to
me personally known, who, being by me duly sworn, did say that he is a Vice
President and Treasurer of UNION ELECTRIC COMPANY, 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 by authority of its Board of Directors, and said JERRE E. BIRDSONG
acknowledged said instrument to be the free act and deed of said corporation.

       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/ Debby Anzalone
                                          --------------------------------------
                                            NOTARY PUBLIC - STATE OF MISSOURI
                                           MY COMMISSION EXPIRES APRIL 18, 2006
                                                     ST. LOUIS COUNTY

                                  [NOTARY SEAL]

                                       21
<Page>

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

       On this 5th day of March 2003, before me appeared BELINDA BROWN, to me
personally known, who, being by me duly sworn, did say that she is a 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 Vice
President, 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/ Renee Beard
                                          --------------------------------------
                                            NOTARY PUBLIC - STATE OF MISSOURI
                                           MY COMMISSION EXPIRES JUNE 22, 2006
                                                     ST. LOUIS COUNTY

                                  [NOTARY SEAL]

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Exhibit 10.(a)    
  

[LOGO]

	 	 	Memo
	

	

DATE:	
 	

March 11, 2003
	TO:	 	Tender Offer Participants
	FROM:	 	John Sundeen
	SUBJECT:	 	Tender Offer Reminder

Keith
Tucker and I would like to remind you that the Tender Offer expires Friday of this week. If you want to participate, please turn in your transmittal document to the Legal Department by the close
of business Friday. 

If
you have any questions about the tender offer, please contact any of the following people in the Human Resources Department: 

Bill
Howey 913/236-1902 

Sara
Kircher 913/236-1903 

Patti
Hare 913/236-1905 

Karen
Bulk 913/236-2241 

Amy
Goodman 913/236-1906 

QuickLinks

Exhibit 10.(a)

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00047-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00047-of-00352.parquet"}]]