<PAGE>   1
                                                                   EXHIBIT 10.73



================================================================================


                  LIMITED LIABILITY COMPANY OPERATING AGREEMENT

                                       OF

                                  APERION LLC,

                      A DELAWARE LIMITED LIABILITY COMPANY

                                  JUNE 15, 1999


================================================================================


NEITHER THE UNITED STATES SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE
REGULATORY AUTHORITY HAS APPROVED OR DISAPPROVED THIS LIMITED LIABILITY COMPANY
OPERATING AGREEMENT OR THE LIMITED LIABILITY COMPANY MEMBERSHIP INTERESTS
("INTERESTS") PROVIDED FOR HEREIN. ANY REPRESENTATION TO THE CONTRARY IS
UNLAWFUL.

THE INTERESTS HAVE NOT BEEN REGISTERED UNDER THE UNITED STATES SECURITIES ACT OF
1933, AS AMENDED, INCLUDING THE RULES AND REGULATIONS THEREUNDER (THE
"SECURITIES ACT"), AND THE COMPANY IS UNDER NO OBLIGATION TO REGISTER THE
INTERESTS UNDER THE SECURITIES ACT IN THE FUTURE.

AN INTEREST MAY NOT BE SOLD, PLEDGED, HYPOTHECATED OR OTHERWISE TRANSFERRED IN
THE ABSENCE OF AN EFFECTIVE REGISTRATION UNDER THE SECURITIES ACT OR AN OPINION
OF COUNSEL SATISFACTORY TO THE COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED.
ADDITIONAL RESTRICTIONS ON THE TRANSFER OF INTERESTS ARE CONTAINED IN ARTICLE XI
OF THIS AGREEMENT. BASED UPON THE FOREGOING, EACH ACQUIRER OF AN INTEREST MUST
BE PREPARED TO BEAR THE ECONOMIC RISK OF INVESTMENT THEREIN FOR AN INDEFINITE
PERIOD OF TIME.



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                                TABLE OF CONTENTS



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ARTICLE I FORMATION OF LIMITED LIABILITY COMPANY.................................................................1

         1.1      Formation......................................................................................1
         1.2      Name and Principal Place of Business...........................................................1
         1.3      Office for Records and Agent for Service of Process............................................1
         1.4      Agreement......................................................................................1
         1.5      Purposes.......................................................................................1
         1.6      Definitions....................................................................................2
         1.7      Term...........................................................................................2

ARTICLE II MEMBERSHIP............................................................................................2

         2.1      Members........................................................................................2
         2.2      Representations and Warranties.................................................................2
         2.3      Participation..................................................................................2
         2.4      Substitute Members.............................................................................3
         2.5      Additional Members.............................................................................3
         2.6      Resignation or Withdrawal of a Member..........................................................3
         2.7      Bankruptcy of Dissolution of a Member..........................................................3
         2.8      Rights of Dissociated Member...................................................................3
         2.9      No Contracts...................................................................................3
         2.10     Other Ventures and Activities..................................................................4
         2.11     Member Expenses................................................................................4
         2.12     Member Compensation............................................................................4
         2.13     Tax Matters....................................................................................4

ARTICLE III CONTRIBUTIONS TO CAPITAL.............................................................................5

         3.1      Capital Commitments............................................................................5
         3.2      Equalizing Contributions.......................................................................6
         3.3      Additional Contributions and Loans.............................................................6
         3.4      Interest.......................................................................................6
         3.5      Failure To Make Capital Contribution...........................................................6

ARTICLE IV ACTION BY MEMBERS.....................................................................................6

         4.1      Meetings of Members............................................................................6
         4.2      Voting Standard................................................................................7

ARTICLE V OVERSIGHT, RESTRICTIONS; EXPENSES......................................................................7

         5.1      Oversight by Board of Managers.................................................................7
         5.2      Number; Vacancies..............................................................................7
         5.3      Meetings of Managers...........................................................................7
         5.4      Voting Procedures..............................................................................8
         5.5      Action Without Meeting.........................................................................8
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                                TABLE OF CONTENTS
                                  (Continued)


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         5.6      Normal Functions of Board of Managers..........................................................8
         5.7      Executive Committee............................................................................9
         5.8      Conflict of Interest Matters..................................................................10
         5.9      Loss of Vote..................................................................................10
         5.10     Manager Compensation and Expenses.............................................................10

ARTICLE VI NOTICES..............................................................................................11

         6.1      Notices.......................................................................................11
         6.2      Waiver of Notice..............................................................................11

ARTICLE VII OFFICERS............................................................................................11

         7.1      Chair.........................................................................................11
         7.2      General Manager...............................................................................11
         7.3      Other Officers................................................................................12
         7.4      Contracts.....................................................................................12

ARTICLE VIII ACCOUNTING AND RECORDS.............................................................................12

         8.1      Financial Statements and Records..............................................................12
         8.2      Inspection of Books...........................................................................12
         8.3      Annual and Monthly Reports....................................................................12
         8.4      Tax Returns...................................................................................13

ARTICLE IX ALLOCATIONS..........................................................................................13

         9.1      Allocation of Net Income or Net Loss..........................................................13
         9.2      Partnership Status............................................................................13

ARTICLE X DISTRIBUTIONS.........................................................................................13

         10.1     Allocation of Distributions among Members.....................................................13
         10.2     Discretionary Distributions...................................................................13
         10.3     No Other Withdrawals..........................................................................13

ARTICLE XI TRANSFERS............................................................................................14

         11.1     Transfer of Membership........................................................................14
         11.2     Transfer Void.................................................................................14
         11.3     Transfer of Control of Member.................................................................14
         11.4     Transfer of Control of Members or their Affiliates............................................14

ARTICLE XII BUY-SELL PROVISION..................................................................................15

         12.1     Application...................................................................................15
         12.2     Procedures....................................................................................16
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                                TABLE OF CONTENTS
                                  (Continued)


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ARTICLE XIII INDEMNIFICATION AND LIMITATION OF LIABILITY........................................................16

         13.1     Indemnification...............................................................................16
         13.2     Limitation of Liability.......................................................................17

ARTICLE XIV TERMINATION.........................................................................................17

         14.1     Termination...................................................................................17
         14.2     Continuance of the Company....................................................................18
         14.3     Authority to Wind Up..........................................................................18
         14.4     Winding Up and Certificate of Cancellation....................................................18
         14.5     Distribution of Assets........................................................................18
         14.6     Effect of Termination.........................................................................19

ARTICLE XV DEFINITIONS..........................................................................................19

         15.1     Definitions...................................................................................19

ARTICLE XVI DISPUTE RESOLUTION..................................................................................23

         16.1     Board of Managers Deadlock....................................................................23
         16.2     Arbitration...................................................................................23

ARTICLE XVII MISCELLANEOUS......................................................................................23

         17.1     Amendment.....................................................................................23
         17.2     Withholding Taxes.............................................................................23
         17.3     Publicity.....................................................................................24
         17.4     Further Assurances............................................................................24
         17.5     Construction..................................................................................24
         17.6     Time..........................................................................................24
         17.7     Headings......................................................................................25
         17.8     Severability..................................................................................25
         17.9     Variation of Terms............................................................................28
         17.10    Governing Law.................................................................................25
         17.11    Binding Effect................................................................................25
         17.12    Entire Agreement..............................................................................25
         17.13    Counterparts..................................................................................25
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                                   APERION LLC


                            LIMITED LIABILITY COMPANY
                               OPERATING AGREEMENT


         THIS LIMITED LIABILITY COMPANY OPERATING AGREEMENT, dated as of June
15, 1999, is by and between the persons listed on the signature page hereto as
members of Aperion LLC, a Delaware limited liability company (the "Company").


                                   ARTICLE I
                     FORMATION OF LIMITED LIABILITY COMPANY

         1.1 Formation. The Members have formed the Company pursuant to the
Delaware Limited Liability Company Act, Title 6, Delaware Code Ann., Section
18-101 et seq. (as amended, the "Act") by causing a certificate of formation
("Certificate") for the Company to be filed with the Delaware Secretary of State
and entering into this Agreement. By this Agreement the Members intend to
establish rules and regulations governing ownership and control of the Company.

         1.2 Name and Principal Place of Business. Unless and until changed in
accordance with this Agreement and the Act, the name of the Company will be
"Aperion LLC". The principal place of business of the Company shall be at 430
Ferguson Drive, Mountain View, California 94043 or such other place as the Board
of Managers may hereafter designate.

         1.3 Office for Records and Agent for Service of Process. The Company
shall maintain an office at which shall be maintained the records required by
Section 18-305 of the Act and an agent for service of process as required by
Section 18-104 of the Act. The office at which shall be maintained the records
required by Section 18-305 of the Act shall be the principal office of
Catalytica, Inc., 430 Ferguson Drive, Mountain View, California 94043, and the
name and address of the agent for service of process shall be CorpAmerica, Inc.,
30 Old Rudnick Lane, Dover, Delaware 19901, or such other person and place as
the Board of Managers may hereafter designate.

         1.4 Agreement. For and in consideration of the mutual covenants herein
contained and for other good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, the Members executing this
Agreement hereby agree to the terms and conditions of this Agreement, as it may
from time to time be amended.

         1.5 Purposes. The purposes of the Company are:

             (a) to pursue all reasonable business opportunities in the Field;
and

             (b) to engage in all other lawful activities helpful, necessary or
appropriate to maximize the ability of the Company to accomplish the foregoing
purposes.

             1.6 Definitions. Terms not otherwise defined in this Agreement
shall have the meanings set forth in Article XV.





<PAGE>   6

         1.7 Term. The Company shall have perpetual existence unless this
Agreement is terminated pursuant to the provisions herein.


                                   ARTICLE II
                                   MEMBERSHIP

         2.1 Members. The initial Members of the Company are each of the two
Persons whose names are set forth on the initial signature page of this
Agreement, each of which is admitted as a Member upon execution and delivery of
this Agreement (the "Initial Members"). Additional signature pages may hereafter
be added by the Board of Managers as appropriate to reflect the admission of
Substitute Members or Additional Members in accordance with the provisions of
this Agreement but not otherwise.

         2.2 Representations and Warranties. Each Member hereby represents and
warrants to the Company and the other Member as follows:

             (a) Authorization. The Member is duly organized, validly existing,
and in good standing under the law of its jurisdiction of organization; it has
full power and authority to execute and enter into this Agreement and to perform
its obligations hereunder; and all actions necessary for the due authorization,
execution, delivery and performance by that Member of this Agreement have been
duly taken. This Agreement has been duly executed and delivered by the Member
and constitutes the legal obligation of the Member enforceable in accordance
with its terms.

             (b) Compliance with Other Instruments. The Member's authorization,
execution, delivery, and performance of this Agreement do not conflict with or
violate any law applicable to the Member or any other agreement or arrangement
to which such Member is a party or by which such Member or such Member's assets
is bound.

             (c) Purchase Entirely for Own Account. The Member is acquiring such
Member's interest in the Company for the Member's own account, not as a nominee
or agent, for investment purposes only and not with a view to or for the resale,
distribution, subdivision or fractionalization thereof. The Member has no
contract, present intention, understanding, undertaking, agreement or
arrangement of any kind with any Person to sell, transfer or pledge to any
Person such Member's interest or any part thereof, nor does such Member have any
plans to enter into any such agreement.

             (d) Investment Experience. The Member has such knowledge and
experience in financial and business matters to be capable of evaluating the
merits and risks of its investment in the Company, is able to bear the economic
risks of an investment in the Company, and is able, without materially impairing
its financial condition, to hold its membership in the Company for an indefinite
period of time and to suffer a complete loss of such investment.

             (e) Disclosure of Information. The Member is aware of the Company's
business affairs and financial condition and has acquired all of the information
about the Company it has requested from the Company and considers necessary to
reach an informed and knowledgeable decision to acquire an interest in the
Company.






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<PAGE>   7

             (f) Federal and State Securities Laws. The Member acknowledges that
the issuance of the membership in the Company has not been registered under the
Securities Act of 1933, as amended (the "Securities Act") or any state
securities laws, inasmuch as they are being acquired in a transaction not
involving a public offering, and under such laws, may not be resold or
transferred by the Member without appropriate registration or the availability
of an exemption from such requirements. In this connection, the Member
represents that it is familiar with Rule 144 promulgated under the Securities
Act, as presently in effect, and understands the resale limitations imposed
thereby and by the Securities Act. The Member is an "accredited investor" within
the meaning of Regulation D promulgated under the Securities Act of 1933, as
amended.

             (g) Brokers and Finders. The Member has not retained any investment
banker, broker or finder in connection with his, her or its investment in the
Company.

         2.3 Participation. Each Initial Member's Allocation Percentage shall be
*** . Each Member shall be entitled to one vote and to participation in the
profits, losses, capital and distributions of the Company equal to its
Allocation Percentage.

         2.4 Substitute Members. A Substitute Member shall have all the rights
and powers and will be subject to all the restrictions and liabilities of the
Member who Transferred its membership in the Company.

         2.5 Additional Members Additional persons may be admitted to the
Company as Members at whatever times and upon such terms and conditions as the
Board of Managers may determine (including as to Additional Member's Capital
Contribution).

         2.6 Resignation or Withdrawal of a Member. Except as specifically
provided below, and subject to the provisions on Transfer contained in Article
XI, no Member may resign, retire or withdraw from membership in the Company or
withdraw such Member's interest in the capital of the Company prior to the
dissolution and winding up of the Company.

         2.7 Bankruptcy of Dissolution of a Member. The Bankruptcy or
Dissolution of a Member (i) will cause such Member to be dissociated from the
Company (a "Dissociated Member"), (ii) will terminate the continued membership
of such Member in the Company, and (iii) will constitute a Dissolution Event and
cause a dissolution and winding up of the Company pursuant to Article XIV hereof
except as expressly provided therein to the contrary.

         2.8 Rights of Dissociated Member. In the event any Member becomes a
"Dissociated Member", the Dissociated Member (or such Member's legal
representative) shall be entitled to participate in the winding up of the
Company to the same extent as any other Member.

         2.9 No Contracts. Each Member hereby covenants not to use any actual or
apparent authority or power to bind the Company to any contract or commitment,
or to otherwise incur any liability to which the Company will be subject,
without the express authorization of the Board of Managers. Each Member hereby
agrees to indemnify and hold the Company and the


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    Confidential Treatment and filed separately with the Commission.





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other Member(s) harmless for any loss, liability, expense, damage or injury
suffered or sustained by the Company and/or the other Members in consequence of
such Member's exercise of such actual or apparent authority or power to bind the
Company in violation of the restrictions set forth herein. Upon any material
breach of a Member's obligations under this Section, the Company shall have a
right of offset against all distributions under this Agreement payable to such
Member (and all amounts thereafter payable to such Member or any Affiliate of
such Member under any other contract binding on the Company) for amounts owed to
the Company pursuant to the indemnification described in the preceding sentence.

         2.10 Other Ventures and Activities.

              (a) The Members: (i) acknowledge that the Members and their
respective Affiliates are or may be involved in other research and development,
manufacturing, sales or business activities; and (ii) agree that each Member and
its Affiliates may engage for their own accounts and for the accounts of others
in any such ventures and activities. Except as otherwise required by fiduciary
duties, (i) neither the Company nor any Member shall have any right by virtue of
this Agreement or the existence of the Company in and to such ventures or
activities or to the income or profits derived therefrom, and (ii) the Members,
their Affiliates, and other related Persons shall have no duty or obligation to
make any reports to the Members or the Company with respect to any such ventures
or activities.

              (b) Each Member acknowledges that the other Member(s) may be
prohibited from taking action for the benefit of the Company: (i) due to
confidential information acquired or obligations incurred in connection with an
outside activity permitted to such Member or its Affiliates under this Section
2.10, or (ii) in connection with activities undertaken prior to the Effective
Date. No Person shall be liable to the Company or any Member for any failure to
act for the benefit of the Company in consequence of a prohibition described in
the preceding sentence.

         2.11 Member Expenses. No Member shall be reimbursed for expenses
incurred on behalf of, or otherwise in connection with, the Company except to
the extent so provided in any CAT Ancillary Agreement, CombiChem Ancillary
Agreement or this Section. All third-party direct expenses reasonably incurred
by a Member in connection with the preparation, negotiation, execution and
delivery of this Agreement and the aforesaid Ancillary Agreements and otherwise
in connection with the formation of the Company shall be reimbursed by the
Company upon presentation of evidence of such expenses reasonably satisfactory
to the Board of Managers.

         2.12 Member Compensation. Except as provided in a CAT Ancillary
Agreement or a CombiChem Ancillary Agreement, no Member shall be entitled to
compensation for services provided by such Member to, or for the benefit of, the
Company.

         2.13 Tax Matters.

              (a) CombiChem is hereby designated the "tax matters partner" of
the Company within the meaning of Section 6231(a)(7) of the Code. Except to the
extent specifically provided in the Code or the Treasury Regulations (or the
laws of other relevant






                                      -4-
<PAGE>   9

taxing jurisdictions), the tax matters partner shall have exclusive authority to
act for or on behalf of the Company with regard to tax matters, including the
authority to make (or decline to make) any available tax elections.

              (b) Except to the extent otherwise required by applicable law
(disregarding for this purpose any requirement that can be avoided through the
filing of an election or similar administrative procedure), the tax matters
partner shall cause the Company to take the position that the Company is a
"partnership" for federal, state and local income tax purposes and shall cause
to be filed with the appropriate tax authorities any elections or other
documents necessary to give due legal effect to such position. A Member shall
not file (and each Member hereby represents that it has not filed) any income
tax election or other document that is inconsistent with the Company's position
regarding its classification as a "partnership" for applicable federal, state
and local income tax purposes.

              (c) No Member shall file a notice with the United States Internal
Revenue Service under Section 6222(b) of the Code in connection with such
Member's intention to treat an item on such Member's federal income tax return
in a manner which is inconsistent with the treatment of such item on the
Company's federal income tax return unless such Member has, not less than 30
days prior to the filing of such notice, provided all Members with a copy of the
notice and thereafter in a timely manner provides such other information related
thereto as any such Member shall reasonably request.

              (d) Any Member entering into a settlement agreement with the
United States Department of the Treasury which concerns a Company item shall
notify all Members of such settlement agreement and its terms within 60 days
after the date thereof.


                                  ARTICLE III
                            CONTRIBUTIONS TO CAPITAL

         3.1 Capital Commitments. The Members shall make Capital Contributions
to the Company each year in the amount mutually agreed upon in the Annual Budget
established for such year in accordance with Section 5.6(a) hereof, as the same
may be amended from time to time by the Board of Managers during the year. To
the extent agreed in the Annual Budget, such Capital Contributions may be made
in the form or cash, property or services. If property is to be contributed,
such contributions shall be equal to the fair market value of the property
contributed and shall be made at or before the time set forth in the Annual
Budget. If services are to be contributed, such services shall be valued in
accordance with the Services Agreement and shall be contributed at or before the
time set forth in the Annual Budget and in conformity with the Services
Agreement. Cash Capital Contributions shall be contributed on an as-needed basis
or on a costs-incurred basis at such time or times as the Board of Managers
determines to be necessary or advisable for the proper and effective functioning
of the Company, and all such cash Capital Contributions shall be made by the
Members in proportion to the total amount of cash Capital Contributions required
to be made by the Members for such year in accordance with the Annual Budget. No
interest shall be required to be paid with respect to any Capital Contribution
made when due under this Agreement regardless of when such amount is required to
be contributed.






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         3.2 Equalizing Contributions. It is intended by the Members that the
Capital Contributions made by the Members each year shall be in proportion to
their Allocation Percentage. Therefore, at the end of each Fiscal Year, at
Dissolution, or at any other time any Member so requests, if the Capital
Contribution by any Member is less than the total Capital Contribution of the
Members multiplied by that Members Allocation Percentage (the "Shortfall
Amount"), that Member shall make an additional Capital Contribution ("Offsetting
Capital Contribution") to the Company in an amount equal to the Shortfall
Amount. Such Offsetting Capital Contribution shall be immediately distributed to
all other Members in such proportions as may be necessary to cause the Capital
Contributions of all Members during the year to be proportional to their
Allocation Percentages.

         3.3 Additional Contributions and Loans. Except for the obligation of
each Member to make an Offsetting Capital Contribution, if required, no Member
shall be permitted or required to make any additional contribution to the
capital of the Company without the consent of the Board of Managers and the
Members. No Member shall lend, or be required to lend, any money to the Company
or guaranty any Company indebtedness unless all Members agree to participate in
such loan or guaranty in proportion to each Member's Allocation Percentage.

         3.4 Interest. No Member shall be entitled to any interest with respect
to such Member's contributions to or share of the capital of the Company or its
share of unallocated Net Income.

         3.5 Failure To Make Capital Contribution. In the event a Member fails
to make a Capital Contribution when due hereunder to satisfy a Capital
Commitment, the other Members (the "Aggrieved Members") may give the
noncontributing Member notice of such failure. If such failure continues for
thirty (30) days after such notice has been given, the Aggrieved Members'
Allocation Percentages shall increase by an amount equal to two times the amount
each Aggrieved Members' Allocation Percentage would increase if the Allocation
Percentage of each Member was recomputed and determined on the basis of the
Capital Contribution of each Member as of that date, and the noncontributing
Member's Allocation Percentage shall decrease by such amount. In addition, the
Aggrieved Members may seek any and all remedies available at law or equity.
Without limitation on the preceding sentences, the Board of Managers may also
require that a noncontributing Member withdraw from its status as a Member for
failing to satisfy a Capital Commitment.


                                   ARTICLE IV
                                ACTION BY MEMBERS

         4.1 Meetings of Members. Meetings of Members may be held for any
purpose at the request of any Member. Members may participate in a meeting of
the Members by means of conference telephone or similar communications equipment
by means of which all persons participating in the meeting can hear each other,
and such participation in a meeting shall constitute presence in person at the
meeting.






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         4.2 Voting Standard. At any duly noticed meeting at which a quorum is
present, the vote of the Member(s) holding an Allocation Percentage of *** or
greater in the aggregate shall decide any question brought before the meeting,
except to the extent that the express provisions of law or this Agreement
require a different vote.


                                   ARTICLE V
                        OVERSIGHT, RESTRICTIONS; EXPENSES

         5.1 Oversight by Board of Managers. Except for situations in which the
approval of the Members is required by statute or this Agreement, in accordance
with Section 18-402 of the Act, the Company shall be managed and controlled by
the Managers acting as a "Board of Managers." The Board of Managers may exercise
all powers of the Company and do all such lawful acts and things that are not by
statute, the Certificate or this Agreement, directed or required to be exercised
or done by the Members themselves. It is intended that the powers and authority
of the Board of Managers shall be substantially the same as the powers and
authority of a board of directors of a corporation formed under the laws of the
State of Delaware. Notwithstanding the foregoing, the Board of Managers may not
do or permit to be done any of the following without the approval of the
Members:

              (a) Any act or thing that the Act or this Agreement requires to be
approved, consented to or authorized by the Members;

              (b) Voluntarily cause the dissolution of the Company;

              (c) Compromise the liability of any Member for improper
distributions; or

              (d) Sell all or a substantial part of the Company's assets, other
than in the ordinary course of business.

         5.2 Number; Vacancies. The Board of Managers shall be comprised of six
(6) Managers, three of whom shall be appointed by CAT (the "CAT Managers") and
three of whom may be appointed by CombiChem (the "CombiChem Managers"). A CAT
Manager may be removed from office by CAT, and a CombiChem Manager may be
removed from office by CombiChem, at any time for any reason. In the event that
any Manager dies, resigns or is removed as a Manager, a substitute manager may
be appointed by the Member that appointed the former Manager whose vacancy is
being filled. On the Effective Date, the CAT Managers shall be Norman Smith,
Bruce Scott and Larry Briscoe, and the CombiChem Managers shall be Diana Lees,
Lee McCracken and Robert Zambias.

         5.3 Meetings of Managers. The Board of Managers may hold meetings, both
regular and special, either within or without the State of Delaware. Regular
meetings of the Board of Managers shall be held at least once a month for the
first six (6) months after the Effective Date and at least once every other
month thereafter; such meetings may be held at times and places determined by
the Board of Managers. Special meetings of the Board of Managers may be


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called by any Manager on 72 hours notice to each Manager by any reasonable
means, including but not limited to telephone or facsimile transmission. Subject
to Sections 5.7 and 5.8, at all meetings of the Board of Managers, a majority of
the Managers consisting of at least two CAT Managers and at least two CombiChem
Managers shall constitute a quorum for the transaction of business. If a quorum
is not present at a meeting of the Board of Managers, the Managers present may
adjourn the meeting from time to time, without notice other than announcement at
the meeting, until a quorum shall be present. Managers may participate in a
meeting of the Board of Managers by means of conference telephone or similar
communications equipment by means of which all persons participating in the
meeting can hear each other, and such participation in a meeting shall
constitute presence in person at the meeting, except that, for at least one
meeting held each calendar quarter (which shall be designated by the Chair as
such in advance of the meeting), the Managers must attend in person in order to
participate. Meetings will alternate between the offices of the Members unless
otherwise agreed. The Member hosting any meeting shall appoint a secretary to
the meeting to record the minutes of the meeting, which will be circulated to
the Managers promptly following the meeting for review and comment and then kept
in a minute book for the Company available to all Managers and Members.

         5.4 Voting Procedures. Subject to Sections 5.7 and 5.8, the CAT
Managers shall have, in the aggregate, one (1) vote, and the CombiChem Managers
shall have, in the aggregate, one (1) vote, on each matter coming before the
Board of Managers at a meeting. Each such vote shall be cast by a majority of
the CAT Managers or the CombiChem Managers, as the case may be, in attendance at
the meeting. Subject to Sections 5.7 and 5.8, any proposed action of the Board
of Managers shall require approval by both votes cast at a duly called meeting
of the Board of Managers at which a quorum is present to be effective.

         5.5 Action Without Meeting. Subject to Sections 5.7 and 5.8, any action
required or permitted to be taken at any meeting of the Board of Managers may be
taken without a meeting if all Managers consent thereto in writing, by single or
counterpart writings, and the writing or writings are filed with the minutes of
proceedings of the Board of Managers.

         5.6 Normal Functions of Board of Managers. Without limiting the
generality of Section 5.1, and subject to the other provisions of this
Agreement, the Board of Managers shall perform the functions described herein.

              (a) Prior to October 1, 1999, the Board of Managers shall consider
and approve an "Annual Budget" for the Fiscal Year ending December 31, 1999, and
prior to the end of each Fiscal Year thereafter, the Board of Managers shall
consider and approve an "Annual Budget" for next three Fiscal Years consisting
of at least ***

                                       ***
                                       ***
                                       ***. The Capital Commitment of each
Member in an Annual Budget shall be equal in proportion to each Member's
Allocation Percentage. Upon the Board of Manager's approval of the Annual Budget
for the Fiscal Year ending December 31, 1999, each Member shall then begin
making its Capital Contribution (the


*** Portions of this page have been omitted pursuant to a request for
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                                      -8-
<PAGE>   13

"Initial Contribution Date"). Neither Member shall be obligated to make a
Capital Contribution for any future Fiscal Year unless and until an Annual
Budget has been approved by the Board of Managers.

              (b) The Board of Managers shall oversee the business activities of
the Company and at all times endeavor to operate the Company in a manner
consistent with the Annual Budget.

              (c) The Board of Managers shall oversee, generally or
specifically, the research and development in the Field for third parties and/or
itself.

              (d) The Board of Managers shall determine the best interest of the
Company in all dealings and proposed dealings with third parties and shall
approve, generally or specifically, the terms of any contract, agreement, deed,
lease, promissory note, or other instrument or document to be executed and
delivered by the Company.

              (e) The Board of Managers shall take such steps as are reasonably
necessary and prudent to protect the proprietary rights of the Company in the
data, trade secrets, technical information, know-how, inventions, discoveries
and other proprietary or confidential information of the Company. Such steps may
include (i) filing for patents, trademarks and copyrights when and as
appropriate and (ii) opposing patent, copyright and trademark applications filed
by third parties which may have an adverse impact upon the Company's proprietary
rights. Any such patents, trademarks or copyrights which are issued during the
term of the Company shall be in the name of the Company and shall be the
property of the Company.

         5.7 Executive Committee. The Members may designate two members of the
Board of Managers (one of whom shall be an appointee of CombiChem and one of
whom shall be an appointee of CAT) to constitute an Executive Committee.
CombiChem hereby appoints Lee McCracken to initially serve on the Executive
Committee, and CAT hereby appoints Norman Smith to initially serve on the
Executive Committee. With respect to each member of the Executive Committee, the
Board of Managers may designate an alternate for such member. The alternate of
any member shall be an appointee of the Member who appointed such member. When a
member of the Executive Committee is absent or disqualified, his alternate may
replace him at any meeting of the Executive Committee. The Executive Committee,
to the extent provided in such resolution, shall have and may exercise all of
the authority of the Board of Managers in the management of the Company,
provided the Executive Committee shall not have the authority of the Board of
Managers in reference to increasing the compensation of the General Manager of
the Company; recommending to Members the sale, lease, exchange, mortgage,
pledge, or other disposition of all of substantially all of the property and
assets of the Company or the purchase or acquisition of another entity or assets
if not made in the usual and regular course of its business; recommending to the
Members Dissolution of the Company or a revocation thereof, altering, amending
or repealing this Agreement; electing or removing the General Manager of the
Company or members of the Executive Committee; declaring cash or property
distributions to the Members; or altering, amending or repealing any resolution
of the Board of Managers which by its terms provides that it shall not be
altered, amended or repealed by the Executive Committee. The designation of the
Executive Committee and the delegation thereto of authority shall not operate to
relieve the Board of Managers, or any member of the







                                      -9-
<PAGE>   14

Board of Managers, or any responsibility imposed upon it or him by this
Agreement. The decision and resolution of the Executive Committee must be made
with the unanimous approval of its acting members.

         5.8 Conflict of Interest Matters.If a Member or an Affiliate of a
Member is or will be a party to a contract or an arbitration proceeding under
Section 16.2 in which the Company also is, or is proposed to be, a party, those
Managers designated by that Member shall not participate in the consideration of
or vote upon any proposed action by the Company concerning said contract or
arbitration proceeding. Notwithstanding Sections 5.3, 5.4 and 5.5, in such an
event the quorum for a meeting of the Board of Managers to consider such a
proposal shall be any three (3) Managers, and the proposal shall be considered
approved by the Board of Managers upon the single vote approving the proposal
cast by the participating Managers at such a meeting or upon a written consent
to the proposal signed by all Managers who were eligible to participate in
consideration of the proposal. Without limiting the generality of the foregoing,


              (a) the CAT Managers shall not consider or vote upon any proposal
by which the Company would rescind, waive, modify, enforce or exercise any
remedy under or with respect to the CAT Ancillary Agreements as they relate to
CAT;

              (b) the CAT Managers shall not consider or vote upon any proposal
for the Company to initiate or respond to any arbitration proceeding against CAT
pursuant to Section 16.2 or concerning the conduct of the Company in such a
proceeding;

              (c) the CombiChem Managers shall not consider or vote upon any
proposal by which the Company would rescind, waive, modify, enforce or exercise
any remedy under or with respect to the CombiChem Ancillary Agreements as they
relate to CombiChem; and

              (d) the CombiChem Managers shall not consider or vote upon any
proposal for the Company to initiate or respond to any arbitration proceeding
against CombiChem pursuant to Section 16.2 or concerning the conduct of the
Company in such a proceeding.

         5.9 Loss of Vote. In the event one Member increases its Allocation
Percentage pursuant to Section 3.6(b) on account of the failure of another
Member to make Capital Contributions sufficient to satisfy its Capital
Commitments and, as a result, said Member's Allocation Percentage in not less
than ***, the voting right of the Managers designated by the noncontributing
Member shall be suspended until such time (if ever) as said Member's Allocation
Percentage is greater than ***. Notwithstanding Section 5.3, 5.4 and 5.5, during
any such suspension the quorum for a meeting of the Board of Managers shall be
any three (3) Managers, and the Board of Managers will act upon the single vote
then eligible to be cast or upon a written consent signed by all Managers who
were eligible to participate in the casting of that vote.

         5.10 Manager Compensation and Expenses. The Board of Managers shall
receive no compensation from the Company for their services as Managers, but
each Manager shall be


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                                      -10-
<PAGE>   15

reimbursed for his or her reasonable out-of-pocket expenses incurred in
attending meetings of the Board of Managers and performing related duties of the
office under reasonable reimbursement procedures.


                                   ARTICLE VI
                                     NOTICES

         6.1 Notices. Whenever notice or demand is required to be given to any
Member by the Act, the Certificate or this Agreement, it shall be given in
writing, by mail, addressed to such Member at such Member's address as it
appears on the records of the Company with postage thereon prepaid, and shall be
deemed given three days after it is deposited in the United States mail. Notice
to Members may also be given by facsimile and shall be deemed given upon the
sending thereof with electronic confirmation of receipt.

         6.2 Waiver of Notice. A Member may waive notice, provided that the
waiver is in writing signed by the Member whether before or after the notice is
required to be given.


                                   ARTICLE VII
                                    OFFICERS

         7.1 Chair. The initial Chair of the Board of Managers shall be Lee
McCracken who shall serve in such capacity until the end of Fiscal Year 2001.
Then CAT shall designate one Manager from among the CAT Managers to serve as
Chair of the Board of Managers for a term of two (2) years concurrent with the
next two Fiscal Years. Thereafter the Chair shall be a CombiChem Manager
designated by CombiChem, then a CAT Manager designated by CAT, and so forth for
successive two year terms. In the event a Chair ceases to be a Manager during
his or her term of office as the Chair, the Member which appointed the former
Chair shall designate another Manager to serve as the Chair for the balance of
the former Chair's term. The Chair shall preside at all meetings of the Board of
Managers.

         7.2 General Manager. The Members shall appoint a General Manager of the
Company, who shall receive instructions from and report to the Board of
Managers. The position of General Manager will alternate between a person
nominated by CAT and a person nominated by CombiChem for two-year terms. The
first nomination of a General Manager will be made by CAT and shall be Bruce
Scott who shall serve in such capacity until the end of Fiscal Year 2001. Then
CombiChem shall designate the General Manager to serve for a term of two (2)
years concurrent with the next two Fiscal Years. Thereafter the General Manager
shall be designated by CAT, then designated by CombiChem, and so forth for
successive two year terms. In the event the General Manager ceases service to
the Company during his or her term of office as the General Manager, the Member
which appointed the former General Manager shall designate a replacement to
serve as the General Manager for the balance of the former General Manager's
term. The day to day management duties of the General Manager and any other
management personnel appointed by the Board of Managers shall be as determined
by the Board of Managers. The General Manager shall be the principal executive
officer of the Company, and, subject to the control of the Board of Managers,
shall have general control and supervision of the policies and operations of the
Company and shall see that all orders and resolutions of the Board of Managers
are carried into effect. He or she shall manage and administer the







                                      -11-
<PAGE>   16

Company's business and affairs and perform all duties and exercise powers
usually pertaining to the position of General Manager, and shall perform such
further duties and exercise such further powers as may be assigned to him or her
from time to time by the Board of Managers. Subject to the limitations
established by the Board of Managers, he or she shall have the authority to
sign, subject to further resolution of the Board of Managers, in the name and on
behalf of the Company, checks, orders, contracts, leases, notes, drafts and
other documents and instruments of the Company.

         7.3 Other Officers. The Board of Managers may create such other offices
and elect such other officers as it deems appropriate. Any number of offices may
be held by the same person. The duties of such officers shall be established
from time to time by the Board of Managers.

         7.4 Contracts. After the Effective Date, the Board of Managers shall
expressly designate the General Manager or one or more Managers or officers to
execute and deliver, on behalf of the Company, any contract, agreement, deed,
lease or other document or instrument approved generally or specifically by it,
and any such document or instrument executed and delivered by such an authorized
Person or Persons shall be deemed to have been duly executed and delivered by
the Company. No Member's signature shall be required in connection with
execution and delivery on such documents and instruments by the Company, and
third parties to such documents and instruments shall be entitled to rely upon
the Board of Manager's general or specific approval and delegation of authority
to the signatory or signatories on behalf of the Company without otherwise
ascertaining whether the requirements of this Agreement have been satisfied.


                                  ARTICLE VIII
                             ACCOUNTING AND RECORDS

         8.1 Financial Statements and Records. The Company shall prepare its
financial statements and tax returns using such methods of accounting as the
Board of Managers deems necessary or appropriate. The Company shall maintain
proper and complete books of account and records of the business of the Company,
under the supervision of the Board of Managers, at the Company's principal
office or at such other place or places as may be designated by the Board of
Managers. The Board of Managers shall give notice to each Member of any change
in the location of the books and records.

         8.2 Inspection of Books. The Company's books and records shall be open
to inspection, audit and copying by any Member, or such Member's designated
representative, upon reasonable notice at any time during business hours for any
purpose reasonably related to the Member's interest in the Company. Any
information so obtained shall be kept confidential by the Member except as
required by law.

         8.3 Annual and Monthly Reports. Financial statements of the Company
shall be prepared as of the end of each Fiscal Year and audited by a firm of
independent certified public accountants selected by the Board of Managers,
provided, however, that the Board of Managers may waive the audit requirement at
any time and for any reason. A copy of the annual financial statements shall be
transmitted to the Members within 45 days after the end of each Fiscal Year.







                                      -12-
<PAGE>   17

In addition, the Company shall cause unaudited monthly financial statements,
including a comparison of actual results to the projections found in the Annual
Budget applicable for the reporting period, to be prepared and distributed to
the Members within 30 days after the end of each month beginning with December
1999.

         8.4 Tax Returns. Within 90 days after the end of each Fiscal Year, the
Board of Managers shall file a federal income tax information return and
transmit to each Member a schedule showing such Member's distributive share of
the Company's income, deductions and credits, and all other information
necessary for such Member to timely file its own federal income tax return for
the Fiscal Year. The Board of Managers similarly shall file, and provide
information to the Members regarding, all appropriate state and local income tax
returns.


                                   ARTICLE IX
                                   ALLOCATIONS

         9.1 Allocation of Net Income or Net Loss. For each Accounting Period ,
Net Income or Net Loss of the Company, or items thereof, shall be allocated to
the Members in proportion to each Member's Allocation Percentage.

         9.2 Partnership Status. The Members agree that the Company shall be
treated as a partnership for all U.S. federal income tax purposes.


                                   ARTICLE X
                                  DISTRIBUTIONS

         10.1 Allocation of Distributions among Members. All distributions by
the Company to the Members shall be made in proportion to each Member's
Allocation Percentage at the time of the distribution.

         10.2 Discretionary Distributions. The Board of Managers may cause the
Company to make distributions to the Members in accordance with Section 10.1 in
such amounts and at such times as they shall from time to time determine to be
in the best interests of the Company and its Members; provided, however, that
distribution of an amount equal to any estimated distribution amount set forth
in the Annual Budget for a Fiscal Year shall be presumptively valid if the
Company realized excess cash flow in at least that amount from operations during
that Fiscal Year. If any assets are distributed in kind, then they shall be
distributed on the basis of the fair market value thereof as determined by the
Members, and shall be deemed to have been sold at such fair market value for
purposes of the allocations under Article IX. The Members agree that it is their
intent, if the Board of Managers deem it to not be detrimental to the Company,
to immediately distribute to the Members any milestone payments and royalties
received by the Company from third parties. Any Offsetting Capital Contribution
made by a Member shall be immediately distributed to the other Member.

         10.3 No Other Withdrawals. Except as otherwise expressly provided for
in this Agreement, no withdrawals or distributions shall be required or
permitted.






                                      -13-
<PAGE>   18

                                   ARTICLE XI
                                    TRANSFERS

         11.1 Transfer of Membership. A Member may Transfer all or a portion of
its membership in the Company to another Member. A Member may also Transfer all
or a portion of its membership to a Substitute Member, and the Substitute Member
will be admitted to the Company as a member, only if: (i) the Substitute Member
shall have agreed in writing to assume all of the obligations of the Member with
respect to the membership being so Transferred (including the obligations
imposed hereunder as a condition to any transfer); (ii) the Board of Managers
shall have concluded (which conclusion may be based upon an opinion of counsel
satisfactory to it) that the Transfer will not result in a termination of the
Company for federal or state income tax purposes, result in (or materially
increase the risk of) the Company being taxable as a corporation for federal
income tax purposes, or result in a violation of any law, rule or regulation by
the Member, the Substitute Member, the Company or the other Member(s); and (iii)
all other Member(s) shall have consented to the Transfer, such consent not to be
unreasonably withheld.

         11.2 Transfer Void. Any purported Transfer of a Member's membership in
contravention of this Article XI shall be void and of no effect to, on or
against the Company, any Member, any creditor of the Company or any claimant
against the Company.

         11.3 Transfer of Control of Member. Any Transfer of legal or beneficial
ownership or control of a Member, whether by sale or issuance of the Member's
equity securities, voting trust agreement, irrevocable proxy or otherwise, shall
be deemed an attempted Transfer of the membership by that Member for purposes of
this Article XI in contravention of Section 11.1.

         11.4 Transfer of Control of Members or their Affiliates.

              (a) If there is any Transfer of legal or beneficial ownership or
control of *** , whether by sale or issuance of equity securities, voting trust
agreement, irrevocable proxy or otherwise, *** may, in its sole discretion,
offer to purchase some or all of *** membership in the Company. *** shall
immediately deliver to *** and the Board of Managers on behalf of the Company
written notice of such offer ("Offer Notice"). *** and *** shall have a period
of thirty (30) days following the receipt of the Offer Notice ("Member Option
Period") to negotiate in good faith the terms (including price) on which ***
will purchase *** membership in the Company. If no agreement is reached between
*** and *** within the Member Option Period, *** shall give written notice
("Election Notice") on or before the third business day after the last day of
the Member Option Period that *** elects either (i) to not purchase ***
membership in the Company, or (ii) to purchase *** membership in the Company at
a price to be determined by the process described below. If *** elects to
purchase *** membership interest in the Company, then within sixty (60) days
after the date of the Election Notice *** and *** will each submit to the other
a price (respectively, the "Election Price") for *** membership interest in the
Company, together with the report of an independent appraiser that


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                                      -14-
<PAGE>   19

supports the Election Price. If the higher of the Election Prices is not more
than *** higher than the lower of the Election Prices, then *** will purchase
*** membership interest in the Company at a price that is the *** . If the
preceding sentence does not apply, then the two independent appraisers will
select a third independent appraiser, and the third appraiser shall determine
the price for *** membership interest in the Company within thirty (30) days
after this selection; provided, the price determined by the third appraiser must
be *** . The closing of the purchase of *** membership interest in the Company
by *** shall take place within thirty (30)days after the price of *** membership
interest in the Company has been determined by the process described above.

              (b) If there is any Transfer of legal or beneficial ownership or
control of *** , whether by sale or issuance of equity securities, voting trust
agreement, irrevocable proxy or otherwise, *** may, in its sole discretion,
offer to purchase some or all of *** membership in the Company. *** shall
immediately deliver to *** and the Board of Managers on behalf of the Company
written notice of such offer ("Offer Notice"). *** and *** shall have a period
of thirty (30) days following the receipt of the Offer Notice ("Member Option
Period") to negotiate in good faith the terms (including price) on which ***
will purchase *** membership in the Company. If no agreement is reached between
*** and *** within the Member Option Period, *** shall give written notice
("Election Notice") on or before the third business day after the last day of
the Member Option Period that *** elects either (i) to not purchase ***
membership in the Company, or (ii) to purchase *** membership in the Company at
a price to be determined by the process described below. If *** elects to
purchase *** membership interest in the Company, then within sixty (60) days
after the date of the Election Notice *** and *** will each submit to the other
a price (respectively, the "Election Price") for *** membership interest in the
Company, together with the report of an independent appraiser that supports the
Election Price. If the higher of the Election Prices is not more than *** higher
than the lower of the Election Prices, then *** will purchase *** membership
interest in the Company at a price *** . If the preceding sentence does not
apply, then the two independent appraisers will select a third independent
appraiser, and the third appraiser shall determine the price for *** membership
interest in the Company within thirty (30) days after this selection; provided,
the price determined by the third appraiser must be *** . The closing of the
purchase of *** membership interest in the Company by *** shall take place
within thirty (30)days after the price of *** membership interest in the Company
has been determined by the process described above.


                                  ARTICLE XII
                               BUY-SELL PROVISION

         12.1 Application. The procedures described in this Article XII are
available only so long as there are only two Members admitted to the Company.
Either Member may initiate the procedures, by giving the other Member notice
pursuant to Section 12.2(a), during the ninety


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                                      -15-
<PAGE>   20

(90) days following (i) dissolution of the Company pursuant to Section 14.1 or
(ii) declaration of a Board Deadlock pursuant to Section 16.1. In addition, an
Aggrieved Member under Section 3.6(a) may initiate the procedures, by giving the
other Member notice pursuant to Section 12.2(a), as provided therein.

         12.2 Procedures. If at any time a Member ("Offering Member") desires to
offer to sell some or all of its membership in the Company ("Offered Interest")
to the other Member, such Offering Member shall immediately deliver to the other
Member ("Nonselling Member) and the Board of Managers on behalf of the Company
written notice of such offer ("Offer Notice"). The Offering Member and the
Nonselling Member shall negotiate in good faith the terms (including price) on
which the Nonselling Member will purchase the Offered Interest, if the
Nonselling Member desires to purchase the Offered Interest.


                                  ARTICLE XIII
                   INDEMNIFICATION AND LIMITATION OF LIABILITY

         13.1 Indemnification.

              (a) To the extent permitted by the Act and by law, the Managers,
the Members as such, and the directors, officers, employees and agents of any of
the foregoing (herein collectively referred to as "Indemnitees") shall, in
accordance with this Section, be indemnified and held harmless by the Company
from and against any and all loss, claims, damages, liabilities joint and
several, expenses, judgments, fines, settlements and other amounts arising from
any and all claims (including reasonable legal expenses and reasonable
attorneys' fees), demands, actions, suits or proceedings (civil, criminal,
administrative or investigative) in which the Indemnitee may be involved, as a
party or otherwise, by reason of management of, or involvement in, the affairs
of the Company, or rendering of advice or consultation with respect thereto, or
which relate to the Company, its properties, business or affairs, if (i) such
Indemnitee acted in good faith and in a manner such Indemnitee reasonably
believed to be in, or not opposed to, the best interests of the Company, and
(ii) with respect to any criminal proceeding, such Indemnitee had no reasonable
cause to believe the conduct of such Indemnitee was unlawful. The termination of
a proceeding by judgment, order, settlement, conviction or upon a plea of nolo
contendere, or its equivalent, shall not, of itself, create a presumption that
the Indemnitee did not act in good faith and in a manner which the Indemnitee
reasonably believed to be in, or not opposed to, the best interests of the
Company or that the Indemnitee had reasonable cause to believe that the
Indemnitee's conduct was unlawful (unless there has been a final adjudication in
the proceeding that the Indemnitee did not act in good faith and in a manner
which the Indemnitee reasonably believed to be in or not opposed to the best
interests of the Company; or that the Indemnitee did have reasonable cause to
believe that the Indemnitee's conduct was unlawful).

              (b) The Company may also indemnify any Person who was or is a
party or is threatened to be made a party to any threatened, pending, or
completed action by or in the right of the Company to procure a judgment in its
favor by reason of the fact that such Person is or was an officer, employee or
agent of the Company, against expenses reasonably incurred by such Person in
connection with the defense or settlement of such action, if such Person acted
in good faith and in a manner such Person reasonably believed to be in, or not
opposed to, the best







                                      -16-
<PAGE>   21

interests of the Company, except that indemnification shall be made in respect
of any claim, issue or matter as to which such Person shall have been adjudged
to be liable for misconduct in the performance of the Person's duty to the
Company only to the extent that the court in which such action or suit was
brought, or another court of appropriate jurisdiction, determines upon
application that, despite the adjudication of liability, but in view of all
circumstances of the case, such Person is fairly and reasonably entitled to
indemnity for such expenses which such court shall deem proper. To the extent
that the Person has been successful on the merits or otherwise in defense of any
proceedings referred to herein, or in defense of any claim, issue or matter
therein, the Person shall be indemnified by the Company against expenses
actually and reasonably incurred by the Person in connection therewith.
Notwithstanding the foregoing, no Person shall be entitled to indemnification
hereunder for any conduct arising from the gross negligence or willful
misconduct or reckless disregard in the performance of the Person's duties under
this Agreement.

              (c) Expenses (including attorneys' fees) incurred in defending any
proceeding under Sections 13.1 (a) or (b) shall be paid by the Company in
advance of the final disposition of such proceeding upon receipt of an
undertaking by or on behalf of the Indemnitee or Person to repay such amount if
it shall ultimately be determined that the Indemnitee or Person is not entitled
to be indemnified by the Company as authorized hereunder.

              (d) The indemnification provided by this Section 13.1 shall not be
deemed to be exclusive of any other rights to which any Person may be entitled
under any agreement, or as a matter of law, or otherwise, both as to action in a
Person's official capacity and to action in another capacity.

              (e) The Board of Managers shall have power to purchase and
maintain insurance on behalf of the Company, the Managers, Members, officers,
employees or agents of the Company and any other Indemnitees at the expense of
the Company, against any liability asserted against or incurred by them in any
such capacity whether or not the Company would have the power to indemnify such
Persons against such liability under the provisions of this Agreement.

         13.2 Limitation of Liability. Notwithstanding anything to the contrary
herein contained, the debts, obligations and liabilities of the Company shall be
solely the debts, obligations and liabilities of the Company; and no Manager or
Member shall be obligated personally for any such debt, obligation or liability
of the Company solely by reason of being a Manager or Member of the Company.


                                   ARTICLE XIV
                                   TERMINATION

         14.1 Termination. The Company shall be dissolved, its assets disposed
of, and its affairs wound up upon the first to occur of the following:

              (a) mutual agreement by all Members;







                                      -17-
<PAGE>   22

              (b) the failure of the Board of Managers to agree on an Annual
Budget for any fiscal year;

              (c) the affirmative vote of the Member(s) holding at least *** of
the aggregate Allocation Percentages;

              (d) the entry of a decree of judicial dissolution under the Act;
or

              (e) 90 days following the occurrence of a Dissolution Event.

         The following procedure is available only so long as there are only two
Members admitted to the Company. The Company shall also be dissolved, its assets
disposed of, and its affairs wound up if either Member gives notice to the other
Member of its desire to dissolve the Company at least ninety (90) days prior to
any annual anniversary of the Effective Date; such dissolution of the Company
shall become effective as of the respective anniversary of the Effective Date.

         14.2 Continuance of the Company. Notwithstanding Section 14.1(d), upon
the occurrence of a Dissolution Event, the remaining Member or Members may avoid
dissolution of the Company by electing, within 90 days after a Dissolution
Event, to continue the business of the Company on the same terms as this
Agreement, except if the Dissolution Event is due to a material breach by any
Member, that Member's Allocation Percentage shall be reduced to zero. Expenses
incurred in the continuance of the Company shall be deemed expenses of the
Company.

         14.3 Authority to Wind Up. The Board of Managers shall have all
necessary power and authority required to marshal the assets of the Company, to
pay its creditors and liabilities, to distribute assets and otherwise wind up
the business and affairs of the Company. The Board of Managers shall continue to
conduct the business and affairs of the Company for such period as may be
necessary to allow an exercise of purchase rights under Article XII ( and
consummation of any purchase and sale resulting from the exercise of such
rights) and shall thereafter continue to conduct the business and affairs of the
Company only insofar as such continued operation remains consistent, in the
judgment of the Board of Managers, with an orderly winding up of the Company.

         14.4 Winding Up and Certificate of Cancellation.The winding up of the
Company shall be completed when all debts, liabilities and obligations of the
Company have been paid and discharged or reasonably adequate provision therefor
has been made, and all of the remaining property and assets of the Company have
been distributed to the Members. Upon the completion of winding up of the
Company, a Certificate of Cancellation shall be filed with the Office of the
Secretary of State of Delaware.

         14.5 Distribution of Assets. Upon dissolution and winding up of the
Company, the affairs of the Company shall be wound up and the Company liquidated
by the Board of


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                                      -18-
<PAGE>   23

Managers. Pursuant to such liquidation, the assets of the Company in the form of
intellectual property owned by the Company (other than rights under the CAT
License and the CombiChem License which are addressed in each such license
agreement) shall be distributed in kind, and the other assets of the Company
shall be sold unless the Members shall consent to a distribution in kind of such
other assets. If the Members do not consent to a distribution in kind but the
Board of Managers determines that an immediate sale would be financially
inadvisable, they may defer sale of the Company assets for a reasonable time. If
any assets are distributed in kind, then they shall be distributed on the basis
of the fair market value thereof as determined by appraisal, and shall be deemed
to have been sold at such fair market value for purposes of the allocations
under Article IX. Unless the Members otherwise agree, if any assets are to be
distributed in kind, they shall be distributed to the Members, as
tenants-in-common, in undivided interests in proportion to distributions to
which the Members are entitled under this Section 14.5. The assets of the
Company, whether cash or in kind, shall be distributed as follows in accordance
with the Act:

              (a) to creditors of the Company in the order of priority provided
by law; and

              (b) the Members in proportion to each Member's Allocation
Percentage.

         14.6 Effect of Termination. The Company shall terminate and cease to
exist when all of its assets have been sold and/or distributed and all of its
affairs have been wound up.


                                   ARTICLE XV
                                   DEFINITIONS

         15.1 Definitions. The following terms shall have the meanings set forth
herein for purposes of this Agreement:

              (a) "Accounting Period" shall mean, for each Fiscal Year, the
period beginning January 1 and ending December 31, provided however, that the
first Accounting Period shall commence on the date of formation of the Company,
the last Accounting Period shall end on the date of the final winding up of the
affairs of the Company, and a new Accounting Period shall commence on any date
on which the Company terminates for tax purposes.

              (b) "Act" shall have the meaning set forth in Section 1.1.

              (c) "Allocation Percentage" shall have the meaning set forth in
Section 2.3.

              (d) "Additional Members" shall be those Members who make a Capital
Contribution to the Company after the Effective Date and are not Initial
Members.

              (e) "Affiliate" shall mean, with respect to a specified Person,
(other than a natural person), a Person that directly, or indirectly through one
or more intermediaries, controls or is controlled by, or is under common control
with, the specified Person.

              (f) "Agreement" shall mean this Limited Liability Company
Operating Agreement as the same may be amended from time to time.






                                      -19-
<PAGE>   24

              (g) "Annual Budget" shall mean the budget of income and expenses
for the Company for each Fiscal Year, and related financial information,
approved by the Board of Managers pursuant to Section 5.6 (a).

              (h) "Certificate" shall have the meaning set forth in Section 1.1.

              (i) "Bankruptcy" shall mean, with respect to any Person, that a
petition shall have been filed by or against such Person as a "debtor" and the
adjudication of such Person as a bankrupt under the provisions of the bankruptcy
laws of the United States of America shall have commenced, or that such Person
shall have made an assignment for the benefit of its creditors generally or a
receiver shall have been appointed for substantially all of the property and
assets of such Person.

              (j) "Board of Managers" shall have the meaning set forth in
Section 5.1.

              (k) "Capital Commitment" shall mean, for each Member, the amount
of money and/or property required to be contributed by that Member to the
capital of the Company pursuant to Article III.

              (l) "Capital Contribution" shall mean, for each Member, that
amount of property, services and/or money, or its equivalent, actually
contributed by that Member to the capital of the Company pursuant to Article
III.

              (m) "Carrying Value" means, with respect to any asset, the asset's
adjusted basis for federal income tax purposes, except as follows:

                  (1) The initial Carrying Value of any asset contributed by a
Member to the Company shall be the agreed-upon fair market value of the asset
upon contribution, as determined by the contributing Member and the Company. The
initial Carrying Value of any asset contributed to the Company as a Capital
Contribution shall be set forth in the Annual Budget calling for that Capital
Contribution.

                  (2) In the discretion of the Board of Managers, the Carrying
Values of all assets may be adjusted to equal their respective fair market
values, as determined by the Board of Managers, and the resulting unrecognized
gain or loss allocated to each Member as though such assets had been sold for
their respective fair market values as of the following times: (A) the increase
in a Member's Allocation Percentage in exchange for more than a de minimis
Capital Contribution; and (B) the distribution by the Company to a Member of
more than a de minimis amount of assets, unless all Members receive simultaneous
distributions of either undivided interests in the distributed property or
identical assets in proportion to their Allocation Percentages.

                  (3) The Carrying Values of all assets shall be adjusted to
equal their respective fair market values, as determined by the Board of
Managers, and the resulting unrecognized gain or loss allocated to each Member
as though such assets had been sold for their respective fair market values as
of the following times: (A) the date the Company is liquidated within the
meaning of Treasury Regulation Section 1.704-1 (b)(2)(ii)(g); and (B) the
termination of the Company pursuant to the provisions of this Agreement.






                                      -20-
<PAGE>   25

                  (4) The Carrying Values of assets shall be increased or
decreased to the extent required under Treasury Regulation Section
1.704-1(b)(2)(iv)(m) in the event that the adjusted tax basis of assets is
adjusted pursuant to Code Sections 732, 734 or 743.

                  (5) The Carrying Value of an asset that is distributed
(whether in liquidation of the Company or otherwise) to one or more Members
shall be adjusted to equal its fair market value, as determined by the Board of
Managers, and the resulting unrecognized gain or loss allocated to each Member
as though such asset had been sold for such fair market value.

                  (6) The Carrying Value of an asset shall be adjusted by the
depreciation, amortization or other cost recovery deductions, if any, taken into
account by the Company with respect to such asset in computing Net Profit or Net
Loss.

              (n) "CAT Ancillary Agreements" shall mean the Services Agreement,
the CAT License and all other agreements between CAT and/or its Affiliates and
the Company.

              (o) "CAT" shall mean Catalytica Advanced Technologies, Inc., a
Delaware corporation.

              (p) "CAT License" shall mean that certain License Agreement of
even date herewith between CAT and the Company.

              (q) "Catalytic Materials" shall have the meaning set forth in
Section 1.5.

              (r) "Code" shall mean the Internal Revenue Code of 1986, as
amended.

              (s) "CombiChem Ancillary Agreements" shall mean the Services
Agreement, the CombiChem License and all other agreements between CombiChem
and/or its Affiliates and the Company..

              (t) "CombiChem" shall mean CombiChem, Inc., a Delaware
corporation.

              (u) "CombiChem License" shall mean that certain License Agreement
of even date herewith between CombiChem and the Company.

              (v) "Dissociated Member" shall have the meaning set forth in
Section 2.6.

              (w) "Dissolution" of a Member that is not a natural person shall
mean that such Member has terminated its existence, whether partnership,
corporate or limited liability company, wound up its affairs and dissolved;
provided, however, that a change in the membership of any Member that is a
general partnership shall not constitute "Dissolution" hereunder, whether or not
the Member is deemed technically dissolved for partnership law purposes, so long
as the business of the Member is continued.

              (x) "Dissolution Event" shall mean (i) a material breach by either
Member of such Member's obligations under this Agreement or any of the CAT
Ancillary Agreements or CombiChem Ancillary Agreements that has not been cured
by such Member within ninety (90) days after receiving notice from the other
Member or the Company of such breach or (ii) the







                                      -21-
<PAGE>   26

Bankruptcy or Dissolution of a Member, the occurrence of which terminates the
Member's continued membership in the Company and results in the dissolution and
winding up of the Company under the Act unless the remaining Members (if more
than one) unanimously agree otherwise pursuant to Section 14.2.

              (y) "Effective Date" shall mean the later of (i) the date on which
the Certificate is filed in the office of the Secretary of State of Delaware, or
(ii) the date on which this Agreement is executed and delivered by the Initial
Members, the CAT Ancillary Agreements are executed and delivered by the parties
thereto, and the CombiChem Ancillary Agreements are executed and delivered by
the parties thereto.

              (z) "Field" shall have the meaning set forth in the CAT License
and the CombiChem License.

              (aa) "Fiscal Year" shall mean the period from January 1 to
December 31 of each year, or as otherwise required by law.

              (bb) "Initial Contribution Date" shall have the meaning set forth
in Section 5.6.

              (cc) "Initial Members" shall have the meaning set forth in Section
2.1.

              (dd) "Manager" shall mean a natural person appointed to the Board
of Managers under Article V and who has not resigned or been removed as a
manager pursuant to this Agreement.

              (ee) "Members" shall mean the Initial Members of the Company and
all Substitute Members and Additional Members, but does not include Dissociated
Members.

              (ff) "Net Income or Net Loss" shall mean the net book income or
loss of the Company for any relevant period. The net book income or loss of the
Company shall be computed in accordance with federal income tax principles (i)
under the method of accounting elected by the Company for federal income tax
purposes, (ii) as applied without regard to any recharacterization of
transactions or relationship that might otherwise be required under such tax
principles and (iii) as otherwise adjusted by:

                   (1) including as income or deductions, as appropriate, any
tax-exempt income and related expenses that are neither properly included in the
computation of taxable income nor capitalized for federal income tax purposes;

                   (2) including as a deduction when paid or incurred (depending
on the Company's method of accounting) any amounts utilized to organize the
Company or to promote the sale of (or to sell) an interest in the Company,
except that amounts for which an election is properly made by the Company under
Section 709(b) of the Code shall be accounted for as provided therein; and

                   (3) calculating the gain or loss on disposition of assets and
the depreciation, amortization or other cost-recovery deductions, if any, with
respect to assets by reference to their Carrying Values rather than their
adjusted tax basis.






                                      -22-
<PAGE>   27

              (gg) "Person" shall mean a natural person, partnership (whether
general or limited), limited liability company, trust, estate, association,
corporation, custodian, nominee, or any other individual or entity in its own or
representative capacity, whether domestic or foreign.

              (hh) `Services Agreement" shall mean that certain Services
Agreement of even date herewith between CAT, CombiChem and the Company.

              (ii) "Substitute Member" shall mean any Person to whom a Member's
membership in the Company is Transferred in whole or in part.

              (jj) "Transfer" shall mean any transfer, sale, exchange,
encumbrance, pledge, mortgage, assignment or other disposition, whether
voluntary or involuntary.

              (kk) "Treasury Regulation" shall mean any regulation issued by the
United States Department of the Treasury pursuant or relating to the Code.


                                   ARTICLE XVI
                               DISPUTE RESOLUTION

         16.1 Board of Managers Deadlock. In the event of any deadlock in voting
at a meeting of the Board of Managers regarding any material decision relating
to the Company, any Manager may declare the existence of a deadlocked vote, in
which event the proposal or other subject matter of the deadlocked vote shall be
referred by the Company first to the Executive Committee who shall confer in
good faith in an effort to eliminate the deadlock and otherwise consider the
matter for a period of thirty (30) days following referral. If the deadlock is
not so broken by that date, the Executive Committee shall submit the proposal or
other subject matter of the deadlocked vote to the chief executive officer of
CombiChem and the chief executive officer of Catalytica, Inc., the sole
stockholder of CAT, who shall confer in good faith in an effort to eliminate the
deadlock and otherwise consider the matter for a period of thirty (30) days
following referral. If the deadlock is not so broken by that date, either Member
may declare that a Board Deadlock exists, and exercise the rights provided in
Section 12.1, at any time during the next ninety (90) days.

         16.2 Arbitration. Except as hereinabove provided, any controversy
between the Members and any claim by one Member against the Company or another
Member arising out of or relating to this Agreement, or the breach thereof,
shall be settled by arbitration in San Francisco, California in accordance with
the then-applicable commercial arbitration rules of the American Arbitration
Association. Judgment upon the award rendered may be entered into any court
having jurisdiction thereof. The losing party shall bear the costs and expenses
of such arbitration.








                                      -23-
<PAGE>   28

                                  ARTICLE XVII

                                  MISCELLANEOUS

         17.1 Amendment. Except as provided herein, this Agreement may be
amended only with the written consent of a majority of the Board of Managers and
of Member(s) holding at least *** of the aggregate Allocation Percentages of all
Members.

         17.2 Withholding Taxes.

              (a) The Company shall at all times be entitled to make payments
with respect to any Member in amounts required to discharge any obligation of
the Company to withhold or make payments to any governmental authority with
respect to any federal, state, local or other jurisdictional tax liability of
such Member arising as a result of such Member's interest in the Company. To the
extent each such payment satisfies an obligation of the Company to withhold with
respect to any distribution to a Member on which the Company did not withhold or
with respect to any Member's allocable share of the income of the Company, each
such payment shall be deemed to be a loan by the Company to such Member (which
loan shall be deemed to be immediately due and payable) and shall not be deemed
a distribution to such Member. The amount of such payments made with respect to
such Member, plus interest on each such amount from the date of each such
payment until such amount is repaid to the Company accruing at an interest rate
per annum equal to the Bank of America prime rate from time to time in effect,
shall be repaid to the Company by (i) deduction from any cash distributions made
to such Member pursuant to this Agreement; (ii) deduction from any non-cash
distributions made to such Member, or (iii) earlier payment by such Member to
the Company, in each case as determined by the Board of Managers in its sole
discretion. The Board of Managers may, in its discretion, defer making
distributions to any Member owing amounts to the Company pursuant to this
Section until such amounts are paid to the Company and shall in addition
exercise any other rights of a creditor with respect to such amounts.

              (b) Each Member agrees to indemnify and hold harmless the Company,
the Managers and the Members, from and against any liability for taxes, interest
or penalties that may be asserted by reason of the failure to deduct and
withhold tax on amounts distributable or allocable to said Member. Any amount
payable as indemnity hereunder by a Member shall be paid promptly to the Company
upon request for such payment from the Board of Managers, and if not so paid,
the Board of Managers and the Company shall be entitled to claim against and
deduct all such amounts from the allocated portion of Net Profits of, or from
any distribution due to, the affected Member.

         17.3 Publicity. The Members will mutually and reasonably approve the
timing, content and dissemination of any public announcement, except to the
extent that any such party is not reasonably able to consult in a timely manner
with or obtain the approval of the other parties when disclosures are required
by applicable law; and, provided further, that either party may disclose the
transactions contemplated by this Agreement, the CAT Ancillary Agreements or the
CombiChem Ancillary Agreements and the terms hereof and thereof in connection
with


*** Portions of this page have been omitted pursuant to a request for
    Confidential Treatment and filed separately with the Commission.





                                      -24-
<PAGE>   29


any bona fide corporate finance transaction (including ongoing credit
facilities), the merger or consolidation of a party or any other transaction
effecting a significant change in the ownership or control of a Member or an
Affiliate or all or substantially all of a Member's or an Affiliate's business,
assets or stock, or other similar corporate transaction or purpose not related
to pricing strategies or marketing plans.

         17.4 Further Assurances. The parties agree to execute and deliver any
further instruments or documents and perform any additional acts that are or may
become necessary to effectuate and carry on the Company created by this
Agreement.

         17.5 Construction. Every covenant, term and provision of this Agreement
shall be construed simply according to its fair meaning and not strictly for or
against any Member.

         17.6 Time. In computing any period of time pursuant to this Agreement,
the day of the act, event or default from which the designated period of time
begins to run shall not be included, but the time shall begin to run on the next
succeeding day. The last day of the period so computed shall be included, unless
it is not a business day, in which event the period shall run until the end of
the next business day.

         17.7 Headings. Section and other headings contained in this Agreement
are for reference purposes only and are not intended to describe, interpret,
define, or limit the scope, extent, or intent of this Agreement or any provision
hereof.

         17.8 Severability. Except as otherwise provided in the succeeding
sentence, every provision of this Agreement is intended to be severable, and, if
any term or provision of this Agreement is illegal or invalid for any reason
whatsoever, such illegality or invalidity shall not affect the validity or
legality of the remainder of this Agreement. The preceding sentence of this
Section shall be of no force or effect if the consequence of enforcing the
remainder of this Agreement without such illegal or invalid term or provision
would be to cause Member to lose the material benefit of its economic bargain.

         17.9 Variation of Terms. All terms and any variations thereof shall be
deemed to refer to masculine, feminine, or neuter, singular or plural, as the
identity of the Person or Persons may require.

         17.10 Governing Law. The laws of the State of Delaware shall govern the
validity of this Agreement, the construction of its terms, and the
interpretation of the rights and duties arising hereunder.

         17.11 Binding Effect. Subject to the restrictions on Transfer set forth
in Article XI, this Agreement shall be binding on and inures to the benefit of
the Members and their respective transferees, successors, assigns and legal
representatives.

         17.12 Entire Agreement. This Agreement constitutes the entire agreement
among the parties with respect to the subject matter herein.

         17.13 Counterparts.This Agreement may be executed in one or more
counterparts with the same force and effect as if each of the signatories had
executed the same instrument.


               [Remainder of This Page Intentionally Left Blank]






                                      -25-

<PAGE>   30

         IN WITNESS WHEREOF, all of the Members of Aperion LLC, a Delaware
limited liability company, have executed this Limited Liability Company
Operating Agreement as of the day and year first above written.



                                        MEMBERS:

                                        CATALYTICA ADVANCED TECHNOLOGIES, INC.,
                                        a Delaware Corporation


                                        By:  /s/ Lawrence W. Briscoe
                                           -------------------------------------
                                        Name:  Lawrence W. Briscoe
                                             -----------------------------------
                                        Title:  CFO
                                              ----------------------------------


                                        Address:   430 Ferguson Drive
                                                   Mountain View, CA  94043





                                        COMBICHEM, INC., a Delaware corporation


                                         By: /s/ Vicente Anido, Jr.
                                           -------------------------------------
                                         Name: Vicente Anido, Jr.
                                             -----------------------------------
                                         Title: President and CEO
                                              ----------------------------------

                                        Address:   9050 Camino Santa Fe
                                                   San Diego, CA  92121