<PAGE>   1
                                                                     Exhibit 4.3

                                 AMENDMENT NO. 1

                           DATED AS OF APRIL 20, 2001

                                       TO

                             $32,000,000 THREE YEAR
                  CREDIT AGREEMENT DATED AS OF JANUARY 31, 2001

                                      AMONG

                          GENENCOR INTERNATIONAL, INC.,

                            THE LENDERS PARTY THERETO

                                       AND

                            THE CHASE MANHATTAN BANK
                             AS ADMINISTRATIVE AGENT

                                              PREPARED BY:
                                              UNDERBERG & KESSLER LLP
                                              COUNSEL TO THE SYNDICATION AGENT
                                              MICHAEL C. DWYER, ESQ.
                                              1800 CHASE SQUARE
                                              ROCHESTER, NEW YORK 14604
                                              TELEPHONE:        (716) 258-2825
                                              FAX:              (716) 258-2821
                                              E-MAIL:  mdwyer@underberg-
                                                                kessler.com

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                       AMENDMENT NO. 1 TO CREDIT AGREEMENT
                       -----------------------------------

         AGREEMENT dated as of April 20, 2001 among GENENCOR INTERNATIONAL, INC.
(the "BORROWER"), the Lenders signatory to this Amendment (each a "LENDER") and
THE CHASE MANHATTAN BANK, as Administrative Agent for the Lenders (in such
capacity, together with its successors in such capacity, the "ADMINISTRATIVE
AGENT").

                                 R E C I T A L S

         R.1 The Borrower, The Chase Manhattan Bank, individually and as
Administrative Agent, ABN Amro Bank N.V. and The Bank of New York have entered
into a $32,000,000 Three Year Credit Agreement, dated as of January 31, 2001
(the "CREDIT AGREEMENT").

         R.2 The Borrower desires to amend the Credit Agreement to increase the
aggregate amount of the Commitments to $40,000,000.

         R.3 The parties wish to add Credit Suisse First Boston as a Lender and
to amend the Credit Agreement on the terms and conditions set forth below.

         NOW, THEREFORE, the parties agree as follows:

         1. DEFINITIONS. Except as otherwise set forth herein, as used in this
Amendment, the terms defined in the Credit Agreement shall have the meanings
assigned to them in the Credit Agreement.

         2. AMENDMENTS.  The Credit Agreement is hereby amended as set forth
below:

                  2.1 DEFINITIONS. The following definitions are added to
SECTION 1.01 of the Credit Agreement:

                           "AMENDMENT NO. 1" shall mean Amendment No. 1 dated as
                           of April 20, 2001 to Credit Agreement dated as of
                           January 31, 2001.

                           "LENDERS" means the Persons listed on SCHEDULE 2.01,
                           in the form attached to Amendment No. 1 as EXHIBIT
                           2.1, and any other Person that shall have become a
                           party hereto pursuant to an Assignment and
                           Acceptance, other than such Person that ceases to be
                           a party hereto pursuant to an Assignment and
                           Acceptance.



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                  2.2 DEFINITIONS - COMMITMENT. The definition of Commitment in
SECTION 1.01 is amended to read as follows:

                           "COMMITMENT" means, with respect to each Lender, the
                           commitment of such Lender to make Loans hereunder,
                           expressed in dollars, as such commitment may be (a)
                           reduced from time to time pursuant to SECTION 2.06
                           and (b) reduced or increased from time to time
                           pursuant to assignments by or to such Lender pursuant
                           to SECTION 9.04. The amount of each Lender's
                           Commitment as of the date of Amendment No. 1 is set
                           forth on SCHEDULE 2.01, which Schedule is amended to
                           read as set forth in EXHIBIT 2.2 attached to
                           Amendment No. 1, or in the Assignment and Acceptance
                           pursuant to which such Lender shall have assumed its
                           Commitment, as applicable. The aggregate amount of
                           the Lenders' Commitments as of the date of Amendment
                           No. 1 is $40,000,000.

                  2.3 AMENDMENTS. CLAUSE (vii) is added to SECTION 9.02(b),
which shall read as follows:

                           (vii) amend the provisions of SECTION 9.04(h) except
                           as provided therein;

                  2.4 SPECIAL PURPOSE VEHICLES. SUBPARAGRAPH (h) is added to
SECTION 9.04, which shall read as follows:

                           "(h) Notwithstanding anything to the contrary
                           contained herein, any Lender (a "GRANTING LENDER")
                           may grant to special purpose funding vehicles (each
                           an "SPC") of such Granting Lender, identified as such
                           in writing from time to time by the Granting Lender
                           to the Administrative Agent and the Borrower, the
                           option to provide all or any part of any Loan that
                           such Granting Lender would otherwise be obligated to
                           make pursuant to this Agreement, provided that (i)
                           nothing herein shall constitute a commitment by any
                           SPC to make any Loan, (ii) if an SPC elects not to
                           exercise such option or otherwise fails to provide
                           all or any part of such Loan, the Granting Lender
                           shall be obligated to make such Loan pursuant to the
                           terms hereof, and (iii) except as expressly set forth
                           herein, the rights of any such SPC shall be
                           derivative of the rights of the Granting Lender, and
                           each SPC shall be subject to all of the restrictions
                           upon the Granting Lender herein contained. Each SPC
                           shall be conclusively presumed to have made
                           arrangements with its Granting Lender for the
                           exercise by the Granting Lender of voting and other
                           rights hereunder in a manner which is acceptable to
                           the SPC, and the Administrative Agent, the Lenders
                           and the Borrower and each other party shall be
                           entitled to rely upon and deal solely



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<PAGE>   4

                           with the Granting Lender with respect to Loans made
                           by or through its SPC and with respect to all other
                           matters related to this Agreement. The making of a
                           Loan by an SPC hereunder shall utilize the Commitment
                           of the Granting Lender to the same extent, and as if,
                           such Loan were made by the Granting Lender. Each
                           party hereto hereby agrees that no SPC shall be
                           liable for any indemnity or similar payment
                           obligation under this Agreement (all liability for
                           which shall remain with the related Granting Lender).
                           In furtherance of the foregoing, each party hereto
                           hereby agrees (which agreement shall survive the
                           termination of this Agreement) that, prior to the
                           date that is one year and one day after the payment
                           in full of all outstanding commercial paper or other
                           senior indebtedness of any SPC, it will not institute
                           against, or join any other person in instituting
                           against, such SPC any bankruptcy, reorganization,
                           arrangement, insolvency or liquidation proceedings or
                           similar proceedings under the laws of the United
                           States of America or any state thereof. In addition,
                           notwithstanding anything to the contrary contained in
                           this SECTION 9.04, each SPC may, at any time, without
                           regard to the requirements of SECTION 9.04(b), (i)
                           with notice to, but without the prior written consent
                           of, the Borrower or the Administrative Agent, and
                           without paying any processing fee therefor, assign
                           all or a portion of its interests in any Loans to its
                           Granting Lender (or to any other SPC of such Granting
                           Lender) or to any financial institutions (consented
                           to by the Borrower and the Administrative Agent)
                           providing liquidity and/or credit support to or for
                           the account of such SPC to support the funding or
                           maintenance of Loans made by such SPC (but nothing
                           contained herein shall be construed in derogation of
                           the obligation of the Granting Lender to make Loans),
                           and (ii) disclose on a confidential basis any
                           non-public information relating to its Loans to any
                           rating agency, commercial paper dealer or provider of
                           any surety, guarantee or credit or liquidity
                           enhancement to such SPC. This SECTION 9.04(h) may not
                           be amended without the written consent of all SPC's
                           then designated to the Administrative Agent in
                           accordance with the foregoing provisions of this
                           Section."

         3. REPRESENTATIONS AND WARRANTIES. Borrower hereby represents and
warrants to the Lenders that:

                  3.1 CORPORATE POWER AND AUTHORITY: NO CONFLICTS. The
execution, delivery and performance by the Borrower of this Amendment have been
duly authorized by all necessary corporate action and do not and will not: (a)
require any consent or approval of its shareholders, which has not been
obtained; (b) contravene its charter or by-laws, as amended to date; (c) violate
any provision of, or require any filing,



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<PAGE>   5

registration, consent or approval under, any law, rule, regulation, order, writ,
judgment, injunction, decree, determination or award presently in effect having
applicability to the Borrower or any of its Subsidiaries or Affiliates; (d)
result in a breach of or constitute a default or require any consent that has
not been obtained under any indenture or loan or credit agreement or any other
agreement, lease or instrument to which the Borrower is a party or by which it
or its properties may be bound or affected; (e) result in, or require, the
creation or imposition of any Lien, upon or with respect to any of the
properties now owned or hereafter acquired by the Borrower and its Subsidiaries;
or (f) cause the Borrower (or any Subsidiary or Affiliate, as the case may be),
to be in default under any such law, rule, regulation, order, writ, judgment,
injunction, decree, determination or award or any such indenture, agreement,
lease or instrument.

                  3.2 LEGALLY ENFORCEABLE AGREEMENT. This Amendment, and the
Credit Agreement as amended hereby, are the legal, valid and binding obligations
of the Borrower enforceable against the Borrower in accordance with their
respective terms, except to the extent that such enforcement might be limited by
applicable bankruptcy, insolvency or other similar laws affecting creditors'
rights generally.

                  3.3 NO DEFAULT. On and as of the date of this Amendment, and
after giving effect to this Amendment, no event has occurred and is continuing
which constitutes a Default or Event of Default.

                  3.4 REPRESENTATIONS AND WARRANTIES. All representations and
warranties contained in the Credit Agreement are true and correct as of the date
of this Amendment as if fully set forth herein and made on and as of the date of
this Amendment. The Borrower has heretofore furnished to Credit Suisse First
Boston its consolidated balance sheet and statements of income, stockholders'
equity and cash flows as of and for the fiscal year ended December 31, 2000,
reported on by PricewaterhouseCoopers LLP, independent public accountants. Such
financial statements present fairly, in all material respects, the financial
position and results of operations and cash flows of the Borrower and its
Subsidiaries as of such date and for such period in accordance with GAAP.



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                  3.5 MATERIAL ADVERSE CHANGE. Since December 31, 1999, there
has been no material adverse change in the condition (financial or otherwise),
business, operations or prospects of the Borrower and its Subsidiaries, taken as
a whole.

         4. EFFECTIVENESS. This Amendment shall be of no force or effect unless
and until the date on which all of the following conditions are met:

                  4.1 COUNTERPARTS. The Borrower and the Administrative Agent
have each received counterparts of this Amendment duly executed by the Borrower,
the Administrative Agent, and all of the Lenders.

                  4.2 RESOLUTIONS. The Administrative Agent shall have received
certified copies of the resolutions of the board of directors of the Borrower,
in form and content reasonably satisfactory to the Administrative Agent,
authorizing the execution, delivery and performance of this Amendment.

         5. CREDIT SUISSE/OUTSTANDING BORROWINGS. Upon this Amendment becoming
effective, Credit Suisse First Boston shall become a Lender and shall have all
of the rights, duties and obligations of a Lender, and it shall make such Loans
to the Borrower as may be necessary so that all Borrowings outstanding
immediately prior to the execution of this Amendment are held by all Lenders
ratably in accordance with their respective Commitments, after giving effect to
this Amendment.

         6. CHASE'S EXPENSES. Borrower agrees to pay The Chase Manhattan Bank
("CHASE") for all costs, expenses and charges (including, without limitation,
fees and charges of external legal counsel for Chase and costs allocated by its
internal legal department) incurred by Chase in connection with the negotiation,
preparation and execution of this Amendment and other documents executed in
connection herewith.

         7. MISCELLANEOUS. Except as expressly provided in this Amendment, the
Credit Agreement shall remain unchanged and in full force and effect, except
that each reference in the Credit Agreement, and in any agreements, certificates
and notices simultaneously herewith or hereafter executed under or pursuant to
the Credit Agreement, to the "Credit Agreement", "this Agreement", "hereof",
"herein" and similar terms referring to the Credit Agreement, shall be deemed to
refer to the Credit Agreement as amended by this Amendment.



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         This Amendment shall be governed by and construed in accordance with
the laws of the State of New York applicable to contracts made and to be
performed in such state, without regard to conflict of laws principles.

         The section headings in this Amendment are inserted for convenience
only and shall not be a part of this instrument.

         This Amendment may be signed in any number of counterparts, each of
which shall be an original, with the same effect as if the signature thereto and
hereto were upon the same instrument.

SIGNATURE PAGES S-1 to S-5 TO FOLLOW.

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                                                                             S-1

         IN WITNESS WHEREOF, the parties have caused this Amendment to be
executed as of the date first above written.

                                          GENENCOR INTERNATIONAL, INC.


                                          By  /s/ Raymond J. Land
                                              ------------------------------
                                          Name:  Raymond J. Land
                                          Title: Senior Vice President
                                                 Chief Financial Officer

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                                                                             S-2

                                          THE CHASE MANHATTAN BANK, individually
                                          and as Administrative Agent

                                          By  /s/ Scott Rose
                                              ----------------------------------
                                          Name:  Scott Rose
                                          Title: Vice President


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                                                                             S-3

                                          BANKS:
                                          ABN AMRO BANK N.V.



                                          By  /s/ Angela Noique
                                              ----------------------------------
                                            Name:  Angela Noique
                                            Title: Vice President

                                          By  /s/ John J. Mack
                                              ----------------------------------
                                            Name:  John J. Mack
                                            Title: Group Vice President

                                      -10-

<PAGE>   11


                                                                             S-4

                                          BANKS:
                                          THE BANK OF NEW YORK

                                          By:  /s/ David S. Csatari
                                               ---------------------------------
                                            Name:  David S. Csatari
                                            Title: Assistant Vice President






                                      -11-

<PAGE>   12


                                                                             S-5

                                          BANKS:
                                          CREDIT SUISSE FIRST BOSTON

                                          By: /s/ William S. Lutkins
                                              ------------------------------
                                            Name:  William S. Lutkins
                                            Title: Vice President

                                          By: /s/ Robert N. Finney
                                              ------------------------------
                                            Name:  Robert N. Finney
                                            Title: Managing Director

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<PAGE>   13


                                   EXHIBIT 2.2
                                   -----------

                                  SCHEDULE 2.01

                                   COMMITMENTS

Lender                                Commitment
------                                ----------

The Chase Manhattan Bank            $13,333,333.34

ABN Amro Bank N.V.                   12,000,000.00

The Bank of New York                  6,666,666.66

Credit Suisse First Boston            8,000,000.00
                                     -------------

                                     40,000,000.00

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