Document:

<PAGE>   1
                                                                     EXHIBIT 4.3

The Chase Manhattan Bank                                           Scott R. Rose
MMBG                                                              Vice President
One Chase Square, Tower 9
Rochester, NY 14643
Tel: 716-258-0814
Fax: 716-258-0841
                               [CHASE LETTERHEAD]

                                  May 4, 2000

Mr. Andrew Ashworth
Global Treasurer
Genencor International, Inc.
200 Meridian Centre Blvd.
Rochester, NY 14618

Dear Andy:

I am pleased to inform you that The Chase Manhattan Bank (the "Bank") is
prepared, in its sole discretion, to offer a line of credit to Genencor
International, Inc. (the "Borrower") subject to the terms and conditions
described below and in the attached Term Sheet.

Any advances which the Bank may extend will be on the terms and conditions as
we may require at the time the Borrower requests an advance and must be
evidenced by documents in form and substance satisfactory to the Bank.

This line of credit does not constitute a commitment or in any way obligate the
Bank to lend whether or not the Borrower satisfies the conditions stated in
this letter, and is issued subject to the Bank in its sole discretion,
continuing to be satisfied with the Borrower's financial condition and economic
prospects, prompt advice to the Bank of any circumstances which might
materially or adversely affect the Borrower, and the Borrower's maintenance of
a satisfactory relationship with the Bank.

This letter is for the Borrower's information only and is not to be show to or
relied upon by third parties. This letter constitutes the entire understanding
between the Bank and the Borrower and supersedes all prior discussions. The
terms and conditions set forth in this letter shall survive the execution of
the documents evidencing the indebtedness and shall remain in effect so long as
this facility remains in place or any amounts remain outstanding under this
line of credit.

The Bank will consider requests for advances hereunder until the earlier of the
activation of the contemplated revolving credit facility or November 7, 2000,
unless this discretionary line of credit is earlier terminated by the Bank in
its sole discretion.
<PAGE>   2

Mr. Andrew Ashworth
May 4, 2000
Page 2

Please acknowledge your understanding of the foregoing by signing and returning
the enclosed copy of this letter to the undersigned at your earliest
convenience.

We appreciate the opportunity to be of service to you.

                                    Very truly yours,

                                    THE CHASE MANHATTAN BANK

                                    /s/ SCOTT R. ROSE
                                    -----------------------------------
                                    Scott R. Rose
                                    Vice President

SRR/GcorLtrCrdMay00.doc
Enclosure

RECEIPT OF THE FOREGOING LETTER IS HEREBY ACKNOWLEDGED,
TOGETHER WITH ASENT TO THE TERMS THEREOF:

GENENCOR INTERNATIONAL, INC.

By: /s/ RAYMOND J. LAND                                Date: 5/4/00
   --------------------------------------------        -------------------------

Its: Raymond J. Land Sr. Vice President and CFO
    -------------------------------------------

By: /s/ ANDREW P. ASHWORTH
   --------------------------------------------

Its: GLOBAL TREASURER
    -------------------------------------------

<PAGE>   3
                                  [CHASE LOGO]

                          GENENCOR INTERNATIONAL, INC.

                                   TERM SHEET

                               DATED MAY 4, 2000

BORROWER:      Genencor International, Inc.

BANK:          The Chase Manhattan Bank

FACILITY:      $30,000,000 line of credit

PURPOSE:       Support of general corporate purposes

MATURITY:      Payable on a demand basis, but in no event later than the earlier
               of activation of the below R/Cs or November 7, 2000.

INTEREST RATE
OPTIONS:       The Bank's Prime Rate (in minimum borrowing amounts of $10,000)

               The Bank's reserve adjusted London Interbank Offering (LIBO) Rate
               plus 100 basis points for interest periods of one, two, or three
               months, and for amounts not less than $500,000 (maximum of three
               LIBO Rate tranches outstanding at any one time), and in $50,000
               increments.<PAGE>   1
                                PROMISSORY NOTE

                                                                    JUNE 2, 1995
US$ 10,000,000.--

     FOR VALUE RECEIVED, the undersigned ("Payor") promises to pay to the order
of Gist-Brocades International B.V., a corporation of The Netherlands with its
principal office and place of business at Wateringseweg 1, P.O. Box 1, 2600 MA
Delft, The Netherlands ("Payee"), the principal amount of ten million United
States Dollars (US$ 10,000,000.--) with interest thereon at an annual rate
equal to five percent (5%) per annum on the outstanding principal hereof.
Interest shall be computed on the basis of a 360 day year on the actual number
of days the principal is outstanding during each annual interest period.
Interim payments under this Note shall be due and payable in annual
instalments, with the first instalment due on April 15, 1996, and annually on
each April 15 thereafter, with the amount of each interim payment being equal
to the amount received as interest by Payor pursuant to the Amended and
Restated and Substituted Promissory Note dated May 4, 1994 (the "FermPro
Note"), in the original principal amount of ten million United States Dollars
(US$ 10,000,000.--) issued by FermPro Manufacturing, LP to IBIS Limited
Partnership and assigned to Payor on the date hereof. All interim payments
received shall be applied to the payment of accrued interest hereon. Payments
of accrued interest will only be payable if and to the extent interest is paid
under the FermPro Note; provided accrued and unpaid interest will be payable
upon prepayment or acceleration of this Note as further provided herein. If not
paid earlier pursuant to the terms of this Note, the entire outstanding
principal balance of this Note, plus accrued and unpaid interest in an amount
up to the interest paid under the FermPro Note through the date of payment of
this Note, shall be due and payable on the earlier of June 3, 2000 or the
prepayment in full of the principal of the FermPro Note, whether by
acceleration or voluntary prepayment or at maturity. On each interim payment
date, whether or not any payment is due hereunder, Payor shall provide the
holder with any certificates provided by FermPro Manufacturing, LP in
connection with FermPro's annual payment pursuant to the FermPro Note.

<PAGE>   2
                                      -2-

     All payments set forth herein shall be made in lawful money of the United
States at the address of Payee set forth above or at such other place as may be
designated in writing by the holder hereof.

     Payor agrees not to amend, modify or waive the FermPro Note without the
prior written consent of holder.

     This Note is being made and delivered by Payor to Payee pursuant to Section
2.9 of that certain Purchase Agreement, dated as of June 2, 1995 (the "Purchase
Agreement"), among Genencor International, Inc. a Delaware corporation, and
Royal Gist-Brocades N.V., and is entitled to the benefit of the security, if
any, provided thereby, and of the guarantees of even date herewith of Cultor
Ltd. and Eastman Chemical Company, respectively, and Payee or the holder of this
Note shall have all of the rights in respect hereof set forth in each thereof.

     Upon the happening of an Event of Default (as that term is defined below),
this Note, if not then due, shall at the option of Payee or holder hereof,
become due and payable immediately without demand or notice to Payor or any
endorser or guarantor hereof. Any amount of principal which is not paid when
due, whether at stated maturity, by acceleration or otherwise, shall bear
interest from the date when due until said principal amount is paid in full at
an annual rate equal to the greater of seven percent (7%) or the maximum rate
permitted by applicable law. Payor and all endorsers and guarantors hereof
jointly and severally waive presentment, demand for payment, notice of
dishonour, notice of protest and protest and all other notices or demands in
connection with the delivery, acceptance, performance, default, endorsement or
guaranty of this instrument.

     An Event of Default for the purposes hereof shall occur upon: (1) the
failure of the Payor to make any interest or other payment as and when the same
becomes due in accordance with the terms hereof, which failure continues for ten
(10) days after notice to the Payor that such payment is due and payable; (2)
any breach by Payor of the noncompetition and/or nonassertion undertakings as
they affect Payee and as contained in the Purchase Agreement; (3) the failure of
Payor to deliver the Assets to be transferred by Payor to Payee as set
<PAGE>   3

                                     - 3 -

out in the Purchase Agreement; or (4) the institution of any bankruptcy,
insolvency or receivership proceedings by or on behalf of the Payor, which
proceedings are not stayed or dismissed within thirty (30) days of the filing
thereof.

     This Note may be prepaid in whole or in part by Payor, provided that Payor
first gives seven (7) days' prior notice of such prepayment, by payment to
Payee of an amount equal to the sum of (i) the principal amount of this Note so
to be prepaid, and (ii) accrued and unpaid interest on the Note all in
accordance with the terms hereof.

     This Note shall be prepaid in whole, including all principal, interest and
any accrued cost, all without right of setoff, upon the execution by Payor of
any binding agreement to transfer all or substantially all of those assets of
Payor which were acquired from Payee under the terms of the Purchase Agreement.

     If any payment required by this Note, or any portion thereof, or any
monies owing hereunder to the Payee, is not paid at the time and place
specified therefor, and the Payee employs counsel with respect to the
collection of this Note in relation to any suit or proceeding relating to the
realization of the Payee's rights, powers and/or remedies under this Note, or
to attempt to collect or to enforce this Note against the Payor or any other
party, then, in any such event, all reasonable attorneys' fees arising from
such services, and all reasonable expenses, costs and charges relating thereto
and all other reasonable costs of collection shall be an additional liability
owing hereunder by the Payor to the Payee, payable on demand and bearing
interest, from the date of such demand until payment thereof to the Payee, at
an interest rate per annum equal to the greater of seven percent (7%) or the
maximum rate permitted by applicable law.

     The remedies of the Payee or other holder hereof shall be cumulative and
concurrent, and may be pursued irregularly, successively or together, at the
sole discretion of the holder hereof. No act or omission of the holder, and no
failure to exercise any right or remedy when permitted hereunder shall be
deemed a waiver or release of same.

     Notwithstanding any provision herein, all conflicts under

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                                     - 4 -

or relating to the Purchase Agreement shall be exclusively resolved pursuant to
the terms of that Purchase Agreement.

     This Note shall be governed by and interpreted under the laws of the State
of New York, without giving effect to the principles thereof concerning
conflict of laws.

     IN WITNESS WHEREOF, Payor has executed this Note the day and year first
above written.

                                             GENENCOR INTERNATIONAL, INC.

                                             By: /s/ W. THOMAS MITCHELL
                                               --------------------------------

                                             Name:  W. Thomas Mitchell
                                                  -----------------------------

                                             Title:   Pres/CEO
                                                   ----------------------------

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