**Exhibit 4.3 
**Indianapolis power & light company**

**to**

**THE BANK OF NEW YORK MELLON TRUST COMPANY, N.A.                                                          *****Trustee***

 

 

**Fifty-Seventh Supplemental Indenture**

 

***Dated as of May 1, 2009***

**ESTABLISHING FIRST MORTAGE BONDS,**

**4.90% Series C, Due 2016**
 
**Table of Contents***

**of**

**Fifty-SevenTH Supplemental Indenture**

**of**

**Indianapolis Power & Light Company**

Page

PARTIES............................................................................................................................................................................1RECITALS...........................................................................................................................................................................1SECTION 1          Granting clauses..................................................................................................................................3Part I   Electric Distributing Systems..........................................................................................4Part II  Reserved...........................................................................................................................4 Part III Indeterminate Permits and Franchises........................................................................4 Part IV Other Property................................................................................................................4General and after-acquired title.................................................................................................5SECTION 2          Definitions............................................................................................................................................5SECTION 3        Designation of Fifty-Seventh series of bonds and kind and denominations thereof................6Designation of Company or The Bank of New York Mellon Trust Company, N.A.                    as paying agent                                                                                                                                      Purpose of bonds                                                                                                                                   Redemption of bonds                                                                                                                             Exchange of bonds                                                                                                                                 Transfer of bonds                                                                                                                                   Series limited to $60,000,000                                                                                                                  SECTION 4          Form offully registeredbond..........................................................................................................12Form of Trustee’s certificate onbonds..........................................................................................12SECTION 5         Temporary bonds...............................................................................................................................18SECTION 6          Payment of principal and interest; credits.....................................................................................18SECTION 7          AnnualPayments for Maintenance and ImprovementFund.....................................................18SECTION 8          Compliance with Section 47 of Original Mortgage with respect to dividend restrictions.....19SECTION 9          Acceptance of trusts by Trustee and conditions of acceptance..............................................19SECTION 10         Successors and assigns..................................................................................................................19SECTION 11         Limitation of rights hereunder........................................................................................................19SECTION 12         Compliance with terms, provisions and conditions of Mortgage............................................20SECTION 13         Execution in counterparts...............................................................................................................20TESTIMONIUM..............................................................................................................................................................20SIGNATURES AND SEALS..........................................................................................................................................21ACKNOWLEDGEMENTS..............................................................................................................................................22

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