<PAGE>


                             FIRST SUPPLEMENTAL INDENTURE

     FIRST SUPPLEMENTAL INDENTURE (this "Supplemental Indenture"), dated as
of February 8, 2001, among Argosy of Iowa, Inc. an Iowa corporation, and
Centroplex Centre Convention Hotel, L.L.C., a Louisiana limited liability
company (the "Guaranteeing Subsidiaries"), Argosy Gaming Company, a Delaware
corporation (the "Company"), Alton Gaming Company, an Illinois corporation,
Argosy of Louisiana, Inc., a Louisiana corporation, Catfish Queen Partnership
in Commendam, a Louisiana limited partnership, The Indiana Gaming Company, an
Indiana corporation, Iowa Gaming Company, an Iowa corporation, Jazz
Enterprises, Inc., a Louisiana corporation and The Missouri Gaming Company, a
Missouri corporation (collectively, the "Initial Subsidiary Guarantors" and
together with the Guaranteeing Subsidiaries, the "Subsidiary Guarantors") and
Bank One Trust Company, NA, as trustee under the Indenture referred to below
(the "Trustee").


                                    WITNESSETH

     WHEREAS, the Company and the Initial Subsidiary Guarantors have
heretofore executed and delivered to the Trustee an indenture (the
"Indenture"), dated as of June 8, 1999 providing for the issuance of an
initial principal amount of $200,000,000 of 10 3/4% Senior Subordinated Notes
due 2009 (the "Initial Notes");

     WHEREAS, the Company and the Subsidiary Guarantors have authorized the
issuance of (i) an additional $150,000,000 of the Company's Series A 10 3/4%
Senior Subordinated Notes due 2009 (the "Additional Series A Notes"); (ii) an
additional $150,000,000 of the Company's Series B 10 3/4% Senior Subordinated
Notes due 2009 to be issued in exchange for the Additional Series A Notes if
and when an Exchange Offer is consummated (the "Additional Exchange Notes,"
and together with the Additional Series A Notes, the "Additional Notes") and
(iii) the related guarantees by the Subsidiary Guarantors of the Additional
Notes;

     WHEREAS, the Company desires to issue the Additional Series A Notes, in
accordance with Section 2.02 and Article 4 of the Indenture and the
Additional Exchange Notes in accordance with Sections 2.02 and 2.06(f) of the
Indenture and the Subsidiary Guarantors desire to guarantee the Additional
Series A Notes and the Additional Exchange Notes in accordance with Article II
of the Indenture;

     WHEREAS, the Indenture provides that under certain circumstances the
Guaranteeing Subsidiaries shall execute and deliver to the Trustee a
supplemental indenture pursuant to which the Guaranteeing Subsidiaries shall
unconditionally guarantee all of the Company's Obligations under the Notes (as
defined in the Indenture), including the Additional Notes, and the Indenture
on the terms and conditions set forth herein (the "Subsidiary Guarantee"); and

     WHEREAS, pursuant to Section 9.01 of the Indenture, the Trustee is
authorized to execute and deliver this Supplemental Indenture.



<PAGE>

     NOW THEREFORE, in consideration of the foregoing and for other good and
valuable consideration, the receipt of which is hereby acknowledged, the
parties hereto do hereby mutually covenant and agree as follows:

     1.    CAPITALIZED TERMS.  Capitalized terms used herein without
definition shall have the meanings assigned to them in the Indenture. The
term "Notes" shall have the meanings set forth in the Indenture and shall
include the Initial Notes, the Additional Notes (as defined herein) and any
other Additional Notes (as defined in the Indenture) that may be issued under
the Indenture.

     2.    ADDITIONAL NOTES.

     (a)   ISSUANCE OF ADDITIONAL NOTES.  $150,000,000 aggregate principal
  amount of Additional Series A Notes shall be issued hereunder on the date
  hereof. The Additional Series A Notes shall constitute Additional Notes as
  that term is defined and used in the Indenture.

     (b)   ISSUANCE OF EXCHANGE NOTES.  Upon the consummation of the Exchange
  Offer with respect to the additional Series A Notes, the Additional Exchange
  Notes shall be issued pursuant to Section 2.06(f) of the Indenture solely in
  exchange for Additional Series A Notes, which shall be cancelled upon
  delivery of the Additional Exchange Notes to the Holders of the Additional
  Series A Notes.

     3.    AGREEMENT TO GUARANTEE.  Each of the Guaranteeing Subsidiaries
hereby agrees as follows:

     (a)   Along with all Subsidiary Guarantors named in the Indenture, to
  jointly and severally Guarantee to each Holder of a Note authenticated and
  delivered by the Trustee and to the Trustee and its successors and assigns,
  the Notes or the obligations of the Company hereunder or thereunder, that:

           (i)   the principal of and interest on the Notes will be promptly
      paid in full when due, whether at maturity, by acceleration, redemption
      or otherwise, and interest on the overdue principal of and interest on
      the Notes, if any, if lawful, and all other obligations of the Company
      to the Holders or the Trustee hereunder or thereunder will be promptly
      paid in full or performed, all in accordance with the terms hereof and
      thereof; and

           (ii)  in case of any extension of time of payment or renewal of
      any Notes or any of such other obligations, that same will be promptly
      paid in full when due or performed in accordance with the terms of the
      extension or renewal, whether at stated maturity, by acceleration or
      otherwise. Failing payment when due of any amount so guaranteed or
      any performance so guaranteed for whatever reason, the Subsidiary
      Guarantors shall be jointly and severally obligated to pay the same
      immediately.

     (b)   The obligations hereunder shall be unconditional, irrespective of
  the validity, regularity or enforceability of the Notes or the Indenture,
  the Indenture, the absence of any


                                      2


<PAGE>

  action to enforce the same, any waiver or consent by any Holder of the Notes
  with respect to any provisions hereof or thereof, the recovery of any
  judgment against the Company, any action to enforce the same or any other
  circumstance which might otherwise constitute a legal or equitable
  discharge or defense of a guarantor.

     (c)   The following is hereby waived:  diligence presentment, demand of
  payment, filing of claims with a court in the event of insolvency or
  bankruptcy of the Company, any right to require a proceeding first against
  the Company, protest, notice and all demands whatsoever.

     (d)   This Subsidiary Guarantee shall not be discharged except by
  complete performance of the obligations contained in the Notes and the
  Indenture, and the Guaranteeing Subsidiary accepts all obligations of a
  Subsidiary Guarantor under the Indenture.

     (e)   If any Holder or the Trustee is required by any court or otherwise
  to return to the Company, the Subsidiary Guarantors, or any Custodian,
  Trustee, liquidator or other similar official acting in relation to either
  the Company or the Subsidiary Guarantors, any amount paid by either to the
  Trustee or such Holder, this Subsidiary Guarantee, to the extent theretofore
  discharged, shall be reinstated in full force and effect.

     (f)   The Guaranteeing Subsidiaries shall not be entitled to any right
  of subrogation in relation to the Holders in respect of any obligations
  guaranteed hereby until payment in full of all obligations guaranteed
  hereby.

     (g)   As between the Subsidiary Guarantors, on the one hand, and the
  Holders and the Trustee, on the other hand, (x) the maturity of the
  obligations guaranteed hereby may be accelerated as provided in Article 6
  of the Indenture for the purposes of this Subsidiary Guarantee,
  notwithstanding any stay, injunction or other prohibition preventing
  such acceleration in respect of the obligations guaranteed hereby, and
  (y) in the event of any declaration of acceleration of such obligations as
  provided in Article 6 of the Indenture, such obligations (whether or not
  due and payable) shall forthwith become due and payable by the Subsidiary
  Guarantors for the purpose of this Subsidiary Guarantee.

     (h)   The Subsidiary Guarantors shall have the right to seek
  contribution from any non-paying Subsidiary Guarantor so long as the
  exercise of such right does not impair the rights of the Holders under
  the Guarantee.

     (i)   Pursuant to Section 11.03 of the Indenture, after giving effect
  to any maximum amount and any other contingent and fixed liabilities that
  are relevant under any applicable Bankruptcy or fraudulent conveyance
  laws, and after giving effect to any collections from, rights to receive
  contribution from or payments made by or on behalf of any other Subsidiary
  Guarantor in respect of the obligations of such other Subsidiary
  Guarantor under Article 11 of the Indenture, this new Subsidiary Guarantee
  shall be limited to the maximum amount permissible such that the obligations
  of such Subsidiary


                                      3

<PAGE>

  Guarantor under this Subsidiary Guarantee will not constitute a fraudulent
  transfer or conveyance.

     (j)   Pursuant to Section 11.02 of the Indenture, the obligations of each
  Subsidiary Guarantor under its Subsidiary Guarantee pursuant to Article II
  of the Indenture shall be junior and subordinated to the Senior Indebtedness
  of such Subsidiary Guarantor on the same basis as the Notes are junior and
  subordinated to the Senior Indebtedness of the Company.

     4.    EXECUTION AND DELIVERY.  Each Guaranteeing Subsidiary agrees that
the Subsidiary Guarantees shall remain in full force and effect
notwithstanding any failure to endorse on each Note a notation of such
Subsidiary Guarantee.

     5.    GUARANTEEING SUBSIDIARIES MAY CONSOLIDATE, ETC. ON CERTAIN TERMS.

     (a)   The Guaranteeing Subsidiaries may not consolidate with or merge
  with or into (whether or not such Subsidiary Guarantor is the surviving
  Person) another corporation, Person or entity whether or not affiliated with
  such Subsidiary Guarantor unless:

           (i)   subject to Sections 11.05 and 11.06 of the Indenture, the
      Person formed by or surviving any such consolidation or merger (if
      other than a Subsidiary Guarantor or the Company) unconditionally
      assumes all the obligations of such Subsidiary Guarantor, pursuant to
      a supplemental indenture in form and substance reasonably satisfactory
      to the Trustee, under the Notes, the Indenture and the Subsidiary
      Guarantee on the terms set forth herein or therein; and

           (ii)  immediately after giving effect to such transaction, no
      Default or Event of Default exists.

     (b)   In case of any such consolidation, merger, sale or conveyance and
  upon the assumption by the successor corporation, by supplemental indenture,
  executed and delivered to the Trustee and satisfactory in form to the
  Trustee, of the Subsidiary Guarantee endorsed upon the Notes and the due
  and punctual performance of all of the covenants and conditions of the
  Indenture to be performed by the Subsidiary Guarantor, such successor
  corporation shall succeed to and be substituted for the Subsidiary Guarantor
  with the same effect as if it had been named herein as Subsidiary Guarantor.
  Such successor corporation thereupon may cause to be signed any or all of
  the Subsidiary Guarantees to be endorsed upon all of the Notes issuable
  hereunder which theretofore shall not have been signed by the Company and
  delivered to the Trustee. All the Subsidiary Guarantees so issued shall in
  all respects have the same legal rank and benefit under the Indenture as
  the Subsidiary Guarantees theretofore and thereafter issued in accordance
  with the terms of the Indenture as though all of such Subsidiary Guarantees
  had been issued at the date of the execution hereof.

      (c)  Except as set forth in Articles 4 and 5 and Section 11.05 of
  Article 11 of the Indenture, and notwithstanding clauses (a) and (b) above,
  nothing contained in the Indenture or in any of the Notes shall prevent any
  consolidation or merger of a Subsidiary Guarantor with or into the Company
  or another Subsidiary Guarantor, or shall prevent any sale or conveyance of



                                      4






<PAGE>

the property of a Subsidiary Guarantor as an entirety or substantially as an
entirety to the Company or another Subsidiary Guarantor.

     6. RELEASES.

     (a) In the event of a sale or other disposition of all of the assets of
any Subsidiary Guarantor, by way of merger, consolidation or otherwise, or a
sale or other disposition of all to the capital stock of any Subsidiary
Guarantor, in each case to a Person that is not (either before or after
giving effect to such transaction) a Restricted Subsidiary of the Company,
then such Subsidiary Guarantor (in the event of a sale or other disposition,
by way of merger, consolidation or otherwise, of all of the capital stock of
such Subsidiary Guarantor) or the corporation acquiring the property (in the
event of a sale or other disposition of all or substantially all of the
assets of such Subsidiary Guarantor) will be released and relieved of any
obligations under its Subsidiary Guarantee; PROVIDED that the Net Proceeds of
such sale or other disposition are applied in accordance with the applicable
provisions of the Indenture, including without limitation Section 4.15 of the
Indenture. Upon delivery by the Company to the Trustee of an Officers'
Certificate and an Opinion of Counsel to the effect that such sale or other
disposition was made by the Company in accordance with the provisions of the
Indenture, including without limitation Section 4.15 of the Indenture, the
Trustee shall execute any documents reasonably required in order to evidence
the release of any Subsidiary Guarantor from its obligations under its
Subsidiary Guarantee.

     (b) Any Subsidiary Guarantor not released from its obligations under its
Subsidiary Guarantee shall remain liable for the full amount of principal of
and interest on the Notes and for the other obligations of any Subsidiary
Guarantor under the Indenture as provided in Article 11 of the Indenture.

     7. NO RECOURSE AGAINST OTHERS. No past, present or future director,
officer, employee, incorporator, stockholder or agent of the Guaranteeing
Subsidiary, as such, shall have any liability for any obligations of the
Company or any Guaranteeing Subsidiary under the Notes, any Subsidiary
Guarantees, the Indenture or this Supplemental Indenture or for any claim
based on, in respect of, or by reason of, such obligations or their creation.
Each Holder of the Notes by accepting a Note waives and releases all such
liability. The waiver and release are part of the consideration for issuance
of the Notes. Such waiver may not be effective to waive liabilities under the
federal securities laws and it is the view of the SEC that such a waiver is
against public policy.

     8. NEW YORK LAW TO GOVERN. THE INTERNAL LAW OF THE STATE OF NEW YORK
SHALL GOVERN AND BE USED TO CONSTRUE THIS SUPPLEMENTAL INDENTURE BUT WITHOUT
GIVING EFFECT TO APPLICABLE PRINCIPLES OF CONFLICTS OF LAW TO THE EXTENT THAT
THE APPLICATION OF THE LAWS OF ANOTHER JURISDICTION WOULD BE REQUIRED THEREBY.

     9. COUNTERPARTS. The parties may sign any number of copies of this
Supplemental Indenture. Each signed copy shall be an original, but all of
them together represent the same agreement.


                                     5

<PAGE>

     10. EFFECT OF HEADINGS. The Section headings herein are for convenience
only and shall not affect the construction hereof.

     11. THE TRUSTEE. The Trustee shall not be responsible in any manner
whatsoever for or in respect of the validity or sufficiency of this
Supplemental Indenture or for or in respect of the recitals contained herein,
all of which recitals are made solely by the Guaranteeing Subsidiaries and
the Company.


                            (SIGNATURE PAGE FOLLOWS)




                                      6

<PAGE>

     IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture to be duly executed and attested, all as of the date first above
written.

Dated: February 8, 2001

<TABLE>
<S>                              <C>
                                 ARGOSY OF IOWA, INC.

                                 By: /s/ Dale R. Black
                                     ---------------------
                                     Dale R. Black
                                     Treasurer

                                 CENTROPLEX CENTRE CONVENTION
                                     HOTEL, L.L.C.

                                 By: Arogsy Gaming Company
                                     its Sole Member

                                     By: /s/ Dale R. Black
                                         ---------------------
                                         Dale R. Black
                                         Vice President and
                                         Chief Financial Officer

                                 ARGOSY GAMING COMPANY

                                 By: /s/ Dale R. Black
                                         ---------------------
                                         Dale R. Black
                                         Chief Financial Officer

                                 ALTON GAMING COMPANY

                                 By: /s/ Dale R. Black
                                     ---------------------
                                     Dale R. Black
                                     Treasurer

                                 ARGOSY OF LOUISIANA, INC.

                                 By: /s/ Dale R. Black
                                     ---------------------
                                     Dale R. Black
                                     Treasurer


                                    S-1

<PAGE>

<S>                              <C>
                                 CATFISH QUEEN PARTNERSHIP IN
                                 COMMENDAM

                                 By: ARGOSY OF LOUISIANA, INC.
                                     its General Partner

                                     By: /s/ Dale R. Black
                                         ---------------------
                                         Dale R. Black
                                         Treasurer

                                 THE INDIANA GAMING COMPANY

                                 By: /s/ Dale R. Black
                                     ---------------------
                                     Dale R. Black
                                     Treasurer

                                 IOWA GAMING COMPANY

                                 By: /s/ Dale R. Black
                                     ---------------------
                                     Dale R. Black
                                     Treasurer

                                 JAZZ ENTERPRISES, INC.

                                 By: /s/ Dale R. Black
                                     ---------------------
                                     Dale R. Black
                                     Treasurer

                                 THE MISSOURI GAMING COMPANY

                                 By: /s/ Dale R. Black
                                     ---------------------
                                     Dale R. Black
                                     Treasurer

                                 BANK ONE TRUST COMPANY, NA
                                  as Trustee

                                 By: /s/ Daniel B. Knox
                                     ---------------------
                                     Authorized Signator
</TABLE>

                                 S-2