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                                                                    Exhibit 10.4


                                  MITOKOR, INC.
                             2002 STOCK OPTION PLAN


         1.       ESTABLISHMENT, PURPOSE AND TERM OF PLAN.

                  1.1      ESTABLISHMENT. The MitoKor, Inc. 2002 Stock Option
Plan (the "PLAN") is hereby established effective as of the effective date of
the initial registration by the Company of its Stock under Section 12 of the
Securities Exchange Act of 1934, as amended (the "EFFECTIVE DATE").

                  1.2      PURPOSE. The purpose of the Plan is to advance the
interests of the Participating Company Group and its stockholders by providing
an incentive to attract, retain and reward persons performing services for the
Participating Company Group and by motivating such persons to contribute to the
growth and profitability of the Participating Company Group.

                  1.3      TERM OF PLAN. The Plan shall continue in effect until
the earlier of its termination by the Board or the date on which all of the
shares of Stock available for issuance under the Plan have been issued and all
restrictions on such shares under the terms of the Plan and the agreements
evidencing Awards granted under the Plan have lapsed. However, all Incentive
Stock Options shall be granted, if at all, within ten (10) years from the
earlier of the date the Plan is adopted by the Board or the date the Plan is
duly approved by the stockholders of the Company.

         2.       DEFINITIONS AND CONSTRUCTION.

                  2.1      DEFINITIONS. Whenever used herein, the following
terms shall have their respective meanings set forth below:

                           (a)      "AWARD" means an award of an Option,
Restricted Stock Purchase Right or Restricted Stock Bonus granted under the
Plan.

                           (b)      "AWARD AGREEMENT" means a written agreement
between the Company and a Participant setting forth the terms, conditions and
restrictions of the Award granted to the Participant. An Award Agreement may be
an "Option Agreement," a "Restricted Stock Purchase Agreement," or a "Restricted
Stock Bonus Agreement."

                           (c)      "BOARD" means the Board of Directors of the
Company. If one or more Committees have been appointed by the Board to
administer the Plan, "BOARD" also means such Committee(s).

                           (d)      "CODE" means the Internal Revenue Code of
1986, as amended, and any applicable regulations promulgated thereunder.

                           (e)      "COMMITTEE" means the Compensation Committee
or other committee of the Board duly appointed to administer the Plan and having
such powers as shall be


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specified by the Board. Unless the powers of the Committee have been
specifically limited, the Committee shall have all of the powers of the Board
granted herein, including, without limitation, the power to amend or terminate
the Plan at any time, subject to the terms of the Plan and any applicable
limitations imposed by law.

                           (f)      "COMPANY" means MitoKor, Inc., a Delaware
corporation, or any successor corporation thereto.

                           (g)      "CONSULTANT" means a person engaged to
provide consulting or advisory services (other than as an Employee or a
Director) to a Participating Company, provided that the identity of such person,
the nature of such services or the entity to which such services are provided
would not preclude the Company from offering or selling securities to such
person pursuant to the Plan in reliance on registration on a Form S-8
Registration Statement under the Securities Act.

                           (h)      "DIRECTOR" means a member of the Board or of
the board of directors of any other Participating Company.

                           (i)      "DISABILITY" means the permanent and total
disability of the Participant within the meaning of Section 22(e)(3) of the
Code.

                           (j)      "EMPLOYEE" means any person treated as an
employee (including an Officer or a Director who is also treated as an employee)
in the records of a Participating Company and, with respect to any Incentive
Stock Option granted to such person, who is an employee for purposes of Section
422 of the Code; provided, however, that neither service as a Director nor
payment of a director's fee shall be sufficient to constitute employment for
purposes of the Plan. The Company shall determine in good faith and in the
exercise of its discretion whether an individual has become or has ceased to be
an Employee and the effective date of such individual's employment or
termination of employment, as the case may be. For purposes of an individual's
rights, if any, under the Plan as of the time of the Company's determination,
all such determinations by the Company shall be final, binding and conclusive,
notwithstanding that the Company or any court of law or governmental agency
subsequently makes a contrary determination.

                           (k)      "EXCHANGE ACT" means the Securities Exchange
Act of 1934, as amended.

                           (l)      "FAIR MARKET VALUE" means, as of any date,
the value of a share of Stock or other property as determined by the Board, in
its discretion, or by the Company, in its discretion, if such determination is
expressly allocated to the Company herein, subject to the following:

                                    (i)      If, on such date, the Stock is
listed on a national or regional securities exchange or market system, the Fair
Market Value of a share of Stock shall be the closing price of a share of Stock
(or the mean of the closing bid and asked prices of a share of Stock if the
Stock is so quoted instead) as quoted on the Nasdaq National Market, The Nasdaq


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SmallCap Market or such other national or regional securities exchange or market
system constituting the primary market for the Stock, as reported in THE WALL
STREET JOURNAL or such other source as the Company deems reliable. If the
relevant date does not fall on a day on which the Stock has traded on such
securities exchange or market system, the date on which the Fair Market Value
shall be established shall be the last day on which the Stock was so traded
prior to the relevant date, or such other appropriate day as shall be determined
by the Board, in its discretion.

                                    (ii)     If, on such date, the Stock is not
listed on a national or regional securities exchange or market system, the Fair
Market Value of a share of Stock shall be as determined by the Board in good
faith without regard to any restriction other than a restriction which, by its
terms, will never lapse.

                           (m)      "INCENTIVE STOCK OPTION" means an Option
intended to be (as set forth in the Option Agreement) and which qualifies as an
incentive stock option within the meaning of Section 422(b) of the Code.

                           (n)      "INSIDER" means an Officer, a Director of
the Company or other person whose transactions in Stock are subject to Section
16 of the Exchange Act.

                           (o)      "NONSTATUTORY STOCK OPTION" means an Option
not intended to be (as set forth in the Option Agreement) or which does not
qualify as an Incentive Stock Option.

                           (p)      "OFFICER" means any person designated by the
Board as an officer of the Company.

                           (q)      "OPTION" means a right to purchase Stock
pursuant to the terms and conditions of the Plan. An Option may be either an
Incentive Stock Option or a Nonstatutory Stock Option.

                           (r)      "OPTION AGREEMENT" means a written agreement
between the Company and a Participant setting forth the terms, conditions and
restrictions of the Option granted to the Participant and any shares acquired
upon the exercise thereof. An Option Agreement may consist of a form of "Notice
of Grant of Stock Option" and a form of "Stock Option Agreement" incorporated
therein by reference, or such other form or forms as the Board may approve from
time to time.

                           (s)      "PARENT CORPORATION" means any present or
future "parent corporation" of the Company, as defined in Section 424(e) of the
Code.

                           (t)      "PARTICIPANT" means a person who has been
granted one or more Awards under the Plan.

                           (u)      "PARTICIPATING COMPANY" means the Company or
any Parent Corporation or Subsidiary Corporation.


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                           (v)      "PARTICIPATING COMPANY GROUP" means, at any
point in time, all corporations collectively which are then Participating
Companies.

                           (w)      "RESTRICTED STOCK AWARD" means an Award of a
Restricted Stock Bonus or a Restricted Stock Purchase Right.

                           (x)      "RESTRICTED STOCK BONUS" means Stock granted
to a Participant pursuant to the terms and conditions of Section 7.

                           (y)      "RESTRICTED STOCK PURCHASE RIGHT" means a
right to purchase Stock granted to a Participant pursuant to the terms and
conditions of Section 7.

                           (z)      "RESTRICTION PERIOD" means the period
established in accordance with Section 7.4 during which shares subject to a
Restricted Stock Award are subject to Vesting Conditions.

                           (aa)     "RULE 16b-3" means Rule 16b-3 under the
                                    Exchange Act, as amended from time to time,
                                    or any successor rule or regulation.

                           (bb)     "SECTION 162(m)" means Section 162(m) of the
Code.

                           (cc)     "SECURITIES ACT" means the Securities Act of
1933, as amended.

                           (dd)     "SERVICE" means a Participant's employment
or service with the Participating Company Group, whether in the capacity of an
Employee, a Director or a Consultant. A Participant's Service shall not be
deemed to have terminated merely because of a change in the capacity in which
the Participant renders Service to the Participating Company Group or a change
in the Participating Company for which the Participant renders such Service,
provided that there is no interruption or termination of the Participant's
Service. Furthermore, a Participant's Service shall not be deemed to have
terminated if the Participant takes any military leave, sick leave, or other
bona fide leave of absence approved by the Company; provided, however, that if
any such leave exceeds ninety (90) days, on the ninety-first (91st) day of such
leave the Participant's Service shall be deemed to have terminated unless the
Participant's right to return to Service with the Participating Company Group is
guaranteed by statute or contract. Notwithstanding the foregoing, unless
otherwise designated by the Company or required by law, a leave of absence shall
not be treated as Service for purposes of determining vesting under the
Participant's Agreement. The Participant's Service shall be deemed to have
terminated either upon an actual termination of Service or upon the corporation
for which the Participant performs Service ceasing to be a Participating
Company. Subject to the foregoing, the Company, in its discretion, shall
determine whether the Participant's Service has terminated and the effective
date of such termination.

                           (ee)     "STOCK" means the common stock of the
Company, as adjusted from time to time in accordance with Section 4.2.


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                           (ff)     "SUBSIDIARY CORPORATION" means any present
or future "subsidiary corporation" of the Company, as defined in Section 424(f)
of the Code.

                           (gg)     "TEN PERCENT OWNER" means a Participant who,
at the time an Option is granted to the Participant, owns stock possessing more
than ten percent (10%) of the total combined voting power of all classes of
stock of a Participating Company (other than an Affiliate) within the meaning of
Section 422(b)(6) of the Code.

                           (hh)     "VESTING CONDITIONS" mean those conditions
established in accordance with Section 7.4 prior to the satisfaction of which
shares subject to a Restricted Stock Award remain subject to forfeiture or a
repurchase option in favor of the Company.

                  2.2      CONSTRUCTION. Captions and titles contained herein
are for convenience only and shall not affect the meaning or interpretation of
any provision of the Plan. Except when otherwise indicated by the context, the
singular shall include the plural and the plural shall include the singular. Use
of the term "or" is not intended to be exclusive, unless the context clearly
requires otherwise.

         3.       ADMINISTRATION.

                  3.1      ADMINISTRATION BY THE BOARD. The Plan shall be
administered by the Board. All questions of interpretation of the Plan or of any
Award shall be determined by the Board, and such determinations shall be final
and binding upon all persons having an interest in the Plan or such Award.

                  3.2      AUTHORITY OF OFFICERS. Any Officer shall have the
authority to act on behalf of the Company with respect to any matter, right,
obligation, determination or election which is the responsibility of or which is
allocated to the Company herein, provided the Officer has apparent authority
with respect to such matter, right, obligation, determination or election.

                  3.3      POWERS OF THE BOARD. In addition to any other powers
set forth in the Plan and subject to the provisions of the Plan, the Board shall
have the full and final power and authority, in its discretion:

                           (a)      to determine the persons to whom, and the
time or times at which, Awards shall be granted and the number of shares of
Stock to be subject to each Award;

                           (b)      to designate Options as Incentive Stock
Options or Nonstatutory Stock Options;

                           (c)      to determine the Fair Market Value of shares
of Stock or other property;

                           (d)      to determine the terms, conditions and
restrictions applicable to each Award (which need not be identical) and any
shares acquired upon the exercise thereof, including, without limitation, (i)
the exercise price of the Award, (ii) the method of payment for


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shares purchased upon the exercise of the Award, (iii) the method for
satisfaction of any tax withholding obligation arising in connection with the
Award or such shares, including by the withholding or delivery of shares of
stock, (iv) the timing, terms and conditions of the exercisability of the Award
or the vesting of any shares acquired upon the exercise thereof, (v) the time of
the expiration of the Award, (vi) the effect of the Participant's termination of
Service with the Participating Company Group on any of the foregoing, and (vii)
all other terms, conditions and restrictions applicable to the Award or such
shares not inconsistent with the terms of the Plan;

                           (e)      to approve one or more forms of Agreement;

                           (f)      to amend, modify, extend, cancel or renew
any Award or to waive any restrictions or conditions applicable to any Award or
any shares acquired upon the exercise thereof;

                           (g)      to accelerate, continue, extend or defer the
exercisability of any Award or the vesting of any shares acquired upon the
exercise thereof, including with respect to the period following a Participant's
termination of Service;

                           (h)      to delegate to any proper Officer the
authority to grant one or more Options, without further approval of the Board,
to any person eligible pursuant to Section 5, other than a person who, at the
time of such grant, is an Insider; provided, however, that (i) the exercise
price per share of each such Option shall be equal to the Fair Market Value per
share of the Stock on the effective date of grant, and (ii) each such Option
shall be subject to the terms and conditions of the appropriate standard form of
Agreement approved by the Board and shall conform to the provisions of the Plan
and such other guidelines (including, but not limited to, a limit on the number
of shares for which Options may be granted by an Officer to any one person
during a specified period) as shall be established from time to time by the
Board;

                           (i)      to prescribe, amend or rescind rules,
guidelines and policies relating to the Plan, or to adopt supplements to, or
alternative versions of, the Plan, including, without limitation, as the Board
deems necessary or desirable to comply with the laws of, or to accommodate the
tax policy or custom of, foreign jurisdictions whose citizens may be granted
Awards; and

                           (j)      to correct any defect, supply any omission
or reconcile any inconsistency in the Plan or any Agreement and to make all
other determinations and take such other actions with respect to the Plan or any
Award as the Board may deem advisable to the extent not inconsistent with the
provisions of the Plan or applicable law.

                  3.4      ADMINISTRATION WITH RESPECT TO INSIDERS. With respect
to participation by Insiders in the Plan, at any time that any class of equity
security of the Company is registered pursuant to Section 12 of the Exchange
Act, the Plan shall be administered in compliance with the requirements, if any,
of Rule 16b-3.


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                  3.5      COMMITTEE COMPLYING WITH SECTION 162(m). If the
Company is a "publicly held corporation" within the meaning of Section 162(m),
the Board may establish a Committee of "outside directors" within the meaning of
Section 162(m) to approve the grant of any Award which might reasonably be
anticipated to result in the payment of employee remuneration that would
otherwise exceed the limit on employee remuneration deductible for income tax
purposes pursuant to Section 162(m).

                  3.6      INDEMNIFICATION. In addition to such other rights of
indemnification as they may have as members of the Board or officers or
employees of the Participating Company Group, members of the Board and any
officers or employees of the Participating Company Group to whom authority to
act for the Board or the Company is delegated shall be indemnified by the
Company against all reasonable expenses, including attorneys' fees, actually and
necessarily incurred in connection with the defense of any action, suit or
proceeding, or in connection with any appeal therein, to which they or any of
them may be a party by reason of any action taken or failure to act under or in
connection with the Plan, or any right granted hereunder, and against all
amounts paid by them in settlement thereof (provided such settlement is approved
by independent legal counsel selected by the Company) or paid by them in
satisfaction of a judgment in any such action, suit or proceeding, except in
relation to matters as to which it shall be adjudged in such action, suit or
proceeding that such person is liable for gross negligence, bad faith or
intentional misconduct in duties; provided, however, that within sixty (60) days
after the institution of such action, suit or proceeding, such person shall
offer to the Company, in writing, the opportunity at its own expense to handle
and defend the same.

         4.       SHARES SUBJECT TO PLAN.

                  4.1      MAXIMUM NUMBER OF SHARES ISSUABLE. Subject to
adjustment as provided in Section 4.2, the maximum aggregate number of shares of
Stock that may be issued under the Plan (the "SHARE RESERVE") shall be one
million five hundred thousand (1,500,000) cumulatively increased on January 1,
2003 and each January 1 thereafter (the "ANNUAL INCREASE") by the lesser of (a)
4% of the total number of shares of Stock issued and outstanding on the
preceding December 31, or (b) such lesser number of shares of Stock as
determined by the Board. The Share Reserve shall consist of authorized but
unissued or reacquired shares of Stock or any combination thereof. However,
except as adjusted pursuant to Section 4.2, in no event shall the number of
shares of Stock cumulatively available for issuance pursuant to the exercise of
Incentive Stock Options (the "ISO SHARE LIMIT") exceed one million five hundred
thousand (1,500,000) cumulatively increased by that portion of each Annual
Increase that does not exceed seven hundred thousand (700,000) shares. If an
outstanding Award for any reason expires or is terminated or canceled or if
shares of Stock are acquired upon the exercise of an Award subject to a Company
repurchase option and are repurchased by the Company at the Participant's
exercise price, the shares of Stock allocable to the unexercised portion of such
Award or such repurchased shares of Stock shall again be available for issuance
under the Plan.

                  4.2      ADJUSTMENTS FOR CHANGES IN CAPITAL STRUCTURE. In the
event of any stock dividend, stock split, reverse stock split, spin-off,
recapitalization, combination, reclassification or similar change in the capital
structure of the Company, appropriate adjustments shall be made in the number
and class of shares subject to the Plan and to any


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outstanding Awards, in the ISO Share Issuance Limit set forth in Section 4.1, in
the Section 162(m) Grant Limit set forth in Section 5.4 below, and in the
exercise price per share of any outstanding Awards. If a majority of the shares
which are of the same class as the shares that are subject to outstanding Awards
are exchanged for, converted into, or otherwise become (whether or not pursuant
to an Ownership Change Event, as defined in Section 9.1) shares of another
corporation (the "NEW SHARES"), the Board may unilaterally amend the outstanding
Awards to provide that such Awards are exercisable for New Shares. In the event
of any such amendment, the number of shares subject to, and the exercise price
per share of, the outstanding Awards shall be adjusted in a fair and equitable
manner as determined by the Board, in its discretion. Notwithstanding the
foregoing, any fractional share resulting from an adjustment pursuant to this
Section 4.2 shall be rounded down to the nearest whole number, and in no event
may the exercise price of any Award be decreased to an amount less than the par
value, if any, of the stock subject to the Award. The adjustments determined by
the Board pursuant to this Section 4.2 shall be final, binding and conclusive.

         5.       ELIGIBILITY AND AWARD LIMITATIONS.

                  5.1      PERSONS ELIGIBLE FOR AWARDS. Awards may be granted
only to Employees, Consultants, and Directors. Eligible persons may be granted
more than one (1) Award. However, eligibility in accordance with this Section
shall not entitle any person to be granted an Award, or, having been granted an
Award, to be granted an additional Award.

                  5.2      OPTION GRANT RESTRICTIONS. Any person who is not an
Employee on the effective date of the grant of an Option to such person may be
granted only a Nonstatutory Stock Option.

                  5.3      FAIR MARKET VALUE LIMITATION. To the extent that
options designated as Incentive Stock Options (granted under all stock option
plans of the Participating Company Group, including the Plan) become exercisable
by a Participant for the first time during any calendar year for stock having a
Fair Market Value greater than One Hundred Thousand Dollars ($100,000), the
portions of such options which exceed such amount shall be treated as
Nonstatutory Stock Options. For purposes of this Section 5.3, options designated
as Incentive Stock Options shall be taken into account in the order in which
they were granted, and the Fair Market Value of stock shall be determined as of
the time the option with respect to such stock is granted. If the Code is
amended to provide for a different limitation from that set forth in this
Section 5.3, such different limitation shall be deemed incorporated herein
effective as of the date and with respect to such Options as required or
permitted by such amendment to the Code. If an Option is treated as an Incentive
Stock Option in part and as a Nonstatutory Stock Option in part by reason of the
limitation set forth in this Section 5.3, the Participant may designate which
portion of such Option the Participant is exercising. In the absence of such
designation, the Participant shall be deemed to have exercised the Incentive
Stock Option portion of the Option first. Separate certificates representing
each such portion shall be issued upon the exercise of the Option.

                  5.4      SECTION 162(m) GRANT LIMIT. Subject to adjustment as
provided in Section 4.2, at any such time as the Company is a "publicly held
corporation" within the


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meaning of Section 162(m), no Employee or prospective Employee shall be granted
one or more Awards within any fiscal year of the Company which in the aggregate
are for the purchase of more than one million (1,000,000) shares (the "SECTION
162(m) GRANT LIMIT"). An Award which is canceled in the same fiscal year of the
Company in which it was granted shall continue to be counted against the Section
162(m) Grant Limit for such period

         6.       TERMS AND CONDITIONS OF OPTIONS.

                  Options shall be evidenced by Option Agreements specifying the
number of shares of Stock covered thereby, in such form as the Board shall from
time to time establish. No Option or purported Option shall be a valid and
binding obligation of the Company unless evidenced by a fully executed Option
Agreement. Option Agreements may incorporate all or any of the terms of the Plan
by reference and shall comply with and be subject to the following terms and
conditions:

                  6.1      EXERCISE PRICE. The exercise price for each Option
shall be established in the discretion of the Board; provided, however, that (a)
the exercise price per share for an Incentive Stock Option shall be not less
than the Fair Market Value of a share of Stock on the effective date of grant of
the Option, and (b) no Incentive Stock Option granted to a Ten Percent Owner
shall have an exercise price per share less than one hundred ten percent (110%)
of the Fair Market Value of a share of Stock on the effective date of grant of
the Option. Notwithstanding the foregoing, an Option (whether an Incentive Stock
Option or a Nonstatutory Stock Option) may be granted with an exercise price
lower than the minimum exercise price set forth above if such Option is granted
pursuant to an assumption or substitution for another option in a manner
qualifying under the provisions of Section 424(a) of the Code.

                  6.2      EXERCISABILITY AND TERM OF OPTIONS.

                           (a)      OPTION EXERCISABILITY. Options shall be
exercisable at such time or times, or upon such event or events, and subject to
such terms, conditions, performance criteria and restrictions as shall be
determined by the Board and set forth in the Option Agreement evidencing such
Option; provided, however, that (a) no Option shall be exercisable after the
expiration of ten (10) years after the effective date of grant of such Option,
and (b) no Incentive Stock Option granted to a Ten Percent Owner shall be
exercisable after the expiration of five (5) years after the effective date of
grant of such Option. Subject to the foregoing, unless otherwise specified by
the Board in the grant of an Option, any Option granted hereunder shall
terminate ten (10) years after the effective date of grant of the Option, unless
earlier terminated in accordance with its provisions.

                           (b)      PARTICIPANT RESPONSIBILITY FOR EXERCISE OF
OPTION. Each Participant is responsible for taking any and all actions as may be
required to exercise any Option in a timely manner, and for properly executing
any documents as may be required for the exercise of an Option in accordance
with such rules and procedures as may be established from time to time. By
signing an Option Agreement each Participant acknowledges that information
regarding the procedures and requirements for the exercise of any Option is
available upon such


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Participant's request. The Company shall have no duty or obligation to notify
any Participant of the expiration date of any Option.

                  6.3      PAYMENT OF EXERCISE PRICE.

                           (a)      FORMS OF CONSIDERATION AUTHORIZED. Except as
otherwise provided below, payment of the exercise price for the number of shares
of Stock being purchased pursuant to any Option shall be made (i) in cash, by
check or cash equivalent, (ii) by tender to the Company, or attestation to the
ownership, of shares of Stock owned by the Participant having a Fair Market
Value (as determined by the Company without regard to any restrictions on
transferability applicable to such stock by reason of federal or state
securities laws or agreements with an underwriter for the Company) not less than
the exercise price, (iii) by delivery of a properly executed notice together
with irrevocable instructions to a broker providing for the assignment to the
Company of the proceeds of a sale or loan with respect to some or all of the
shares being acquired upon the exercise of the Option (including, without
limitation, through an exercise complying with the provisions of Regulation T as
promulgated from time to time by the Board of Governors of the Federal Reserve
System) (a "CASHLESS EXERCISE"), (iv) by such other consideration as may be
approved by the Board from time to time to the extent permitted by applicable
law, or (v) by any combination thereof. The Board may at any time or from time
to time, by approval of or by amendment to the standard forms of Option
Agreement described in Section 8, or by other means, grant Options which do not
permit all of the foregoing forms of consideration to be used in payment of the
exercise price or which otherwise restrict one or more forms of consideration.

                           (b)      LIMITATIONS ON FORMS OF CONSIDERATION.

                                    (i)      TENDER OF STOCK. Notwithstanding
the foregoing, an Option may not be exercised by tender to the Company, or
attestation to the ownership, of shares of Stock to the extent such tender or
attestation would constitute a violation of the provisions of any law,
regulation or agreement restricting the redemption of the Company's stock.
Unless otherwise provided by the Board, an Option may not be exercised by tender
to the Company, or attestation to the ownership, of shares of Stock unless such
shares either have been owned by the Participant for more than six (6) months
(and not used for another Option exercise by attestation during such period) or
were not acquired, directly or indirectly, from the Company.

                                    (ii)     CASHLESS EXERCISE. The Company
reserves, at any and all times, the right, in the Company's sole and absolute
discretion, to establish, decline to approve or terminate any program or
procedures for the exercise of Options by means of a Cashless Exercise.

                  6.4      TAX WITHHOLDING. The Company shall have the right,
but not the obligation, to deduct from the shares of Stock issuable upon the
exercise of an Option, or to accept from the Participant the tender of, a number
of whole shares of Stock having a Fair Market Value, as determined by the
Company, equal to all or any part of the federal, state, local and foreign
taxes, if any, required by law to be withheld by the Participating Company Group
with respect to such Option or the shares acquired upon the exercise thereof.
Alternatively or in


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addition, in its discretion, the Company shall have the right to require the
Participant, through payroll withholding, cash payment or otherwise, including
by means of a Cashless Exercise, to make adequate provision for any such tax
withholding obligations of the Participating Company Group arising in connection
with the Option or the shares acquired upon the exercise thereof. The Fair
Market Value of any shares of Stock withheld or tendered to satisfy any such tax
withholding obligations shall not exceed the amount determined by the applicable
minimum statutory withholding rates. The Company shall have no obligation to
deliver shares of Stock or to release shares of Stock from an escrow established
pursuant to the Option Agreement until the Participating Company Group's tax
withholding obligations have been satisfied by the Participant.

                  6.5      EFFECT OF TERMINATION OF SERVICE.

                           (a)      OPTION EXERCISABILITY. Subject to earlier
termination of the Option as otherwise provided herein and unless otherwise
provided by the Board in the grant of an Option and set forth in the Option
Agreement, an Option shall be exercisable after a Participant's termination of
Service only during the applicable time period determined in accordance with
this Section 6.5 and thereafter shall terminate:

                                    (i)      DISABILITY. If the Participant's
Service terminates because of the Disability of the Participant, the Option, to
the extent unexercised and exercisable on the date on which the Participant's
Service terminated, may be exercised by the Participant (or the Participant's
guardian or legal representative) at any time prior to the expiration of one (1)
month (or such longer period of time as determined by the Board, in its
discretion) after the date on which the Participant's Service terminated, but in
any event no later than the date of expiration of the Option's term as set forth
in the Option Agreement evidencing such Option (the "OPTION EXPIRATION DATE").

                                    (ii)     DEATH. If the Participant's Service
terminates because of the death of the Participant, the Option, to the extent
unexercised and exercisable on the date on which the Participant's Service
terminated, may be exercised by the Participant's legal representative or other
person who acquired the right to exercise the Option by reason of the
Participant's death at any time prior to the expiration of one (1) year (or such
longer period of time as determined by the Board, in its discretion) after the
date on which the Participant's Service terminated, but in any event no later
than the Option Expiration Date. The Participant's Service shall be deemed to
have terminated on account of death if the Participant dies within ninety (90)
days (or such longer period of time as determined by the Board, in its
discretion) after the Participant's termination of Service.

                                    (iii)    OTHER TERMINATION OF SERVICE. If
the Participant's Service terminates for any reason, except Disability or death,
the Option, to the extent unexercised and exercisable by the Participant on the
date on which the Participant's Service terminated, may be exercised by the
Participant at any time prior to the expiration of ninety (90) days (or such
longer period of time as determined by the Board, in its discretion) after the
date on which the Participant's Service terminated, but in any event no later
than the Option Expiration Date.


                                       11
<Page>


                           (b)      EXTENSION IF EXERCISE PREVENTED BY LAW.
Notwithstanding the foregoing, if the exercise of an Option within the
applicable time periods set forth in Section 6.5(a) is prevented by the
provisions of Section 11 below, the Option shall remain exercisable until three
(3) months (or such longer period of time as determined by the Board, in its
discretion) after the date the Participant is notified by the Company that the
Option is exercisable, but in any event no later than the Option Expiration
Date.

                           (c)      EXTENSION IF PARTICIPANT SUBJECT TO SECTION
16(b). Notwithstanding the foregoing, if a sale within the applicable time
periods set forth in Section 6.5(a) of shares acquired upon the exercise of the
Option would subject the Participant to suit under Section 16(b) of the Exchange
Act, the Option shall remain exercisable until the earliest to occur of (i) the
tenth (10th) day following the date on which a sale of such shares by the
Participant would no longer be subject to such suit, (ii) the one hundred and
ninetieth (190th) day after the Participant's termination of Service, or (iii)
the Option Expiration Date.

                  6.6      TRANSFERABILITY OF OPTIONS. During the lifetime of
the Participant, an Option shall be exercisable only by the Participant or the
Participant's guardian or legal representative. No Option shall be assignable or
transferable by the Participant, except by will or by the laws of descent and
distribution. Notwithstanding the foregoing, to the extent permitted by the
Board, in its discretion, and set forth in the Option Agreement evidencing such
Option, a Nonstatutory Stock Option shall be assignable or transferable subject
to the applicable limitations, if any, described in the General Instructions to
Form S-8 Registration Statement under the Securities Act.

         7.       TERMS AND CONDITIONS OF RESTRICTED STOCK AWARDS.

                  The Board may from time to time grant Restricted Stock Awards
upon such conditions as the Board shall determine; provided, however, that the
maximum number of shares of Stock which may be issued as Restricted Stock
Bonuses shall not exceed one hundred fifty thousand (150,000). Restricted Stock
Awards may be in the form of either a Restricted Stock Bonus, which shall be
evidenced by Restricted Stock Bonus Agreement, or a Restricted Stock Purchase
Right, which shall be evidenced by Restricted Stock Purchase Agreement. Each
such Award Agreement shall specify the number of shares of Stock subject to and
the other terms, conditions and restrictions of the Award, and shall be in such
form as the Board shall establish from time to time. No Restricted Stock Award
shall be a valid and binding obligation of the Company unless evidenced by a
fully executed Award Agreement. Agreements evidencing Restricted Stock Awards
may incorporate all or any of the terms of the Plan by reference and shall
comply with and be subject to the following terms and conditions:

                  7.1      PURCHASE PRICE. The purchase price under each
Restricted Stock Purchase Right shall be established by the Board; provided,
however, that the purchase price per share shall be not less than the Fair
Market Value of a share of Stock on the effective date of grant of the
Restricted Stock Purchase Right. No monetary payment (other than applicable tax
withholding) shall be required as a condition of receiving a Restricted Stock
Bonus, the


                                       12
<Page>


consideration for which shall be services actually rendered to a Participating
Company or for its benefit.

                  7.2      PURCHASE PERIOD. A Restricted Stock Purchase Right
shall be exercisable within a period established by the Board, which shall in no
event exceed thirty (30) days from the effective date of the grant of the
Restricted Stock Purchase Right.

                  7.3      PAYMENT OF PURCHASE PRICE. Except as otherwise
provided below, payment of the purchase price for the number of shares of Stock
being purchased pursuant to any Restricted Stock Purchase Right shall be made
(i) in cash, by check, or cash equivalent, (ii) by such other consideration as
may be approved by the Committee from time to time to the extent permitted by
applicable law, or (iii) by any combination thereof. The Board may at any time
or from time to time grant Restricted Stock Purchase Rights which do not permit
all of the foregoing forms of consideration to be used in payment of the
purchase price or which otherwise restrict one or more forms of consideration.
Restricted Stock Bonuses shall be issued in consideration for services actually
rendered to a Participating Company or for its benefit.

                  7.4      VESTING AND RESTRICTIONS ON TRANSFER. Shares issued
pursuant to any Restricted Stock Award may be made subject to vesting
conditioned upon the satisfaction of such Service requirements, conditions,
restrictions or performance criteria as shall be established by the Board and
set forth in the Award Agreement evidencing such Award (the "VESTING
CONDITIONS"). During any period (the "RESTRICTION PERIOD") in which shares
acquired pursuant to a Restricted Stock Award remain subject to Vesting
Conditions, such shares may not be sold, exchanged, transferred, pledged,
assigned or otherwise disposed of other than pursuant to an Ownership Change
Event, as defined in Section 9. Upon request by the Company, each Participant
shall execute any agreement evidencing such transfer restrictions prior to the
receipt of shares of Stock hereunder and shall promptly present to the Company
any and all certificates representing shares of Stock acquired hereunder for the
placement on such certificates of appropriate legends evidencing any such
transfer restrictions.

                  7.5      VOTING RIGHTS; DIVIDENDS. Except as provided in this
Section and Section 7.4, during the Restriction Period applicable to shares
subject to a Restricted Stock Award held by a Participant, the Participant shall
have all of the rights of a stockholder of the Company holding shares of Stock,
including the right to vote such shares and to receive all dividends and other
distributions paid with respect to such shares; provided, however, that if any
such dividends or distributions are paid in shares of Stock, such shares shall
be subject to the same Vesting Conditions as the shares subject to the
Restricted Stock Award with respect to which the dividends or distributions were
paid.

                  7.6      EFFECT OF TERMINATION OF SERVICE. Unless otherwise
provided in the grant of a Restricted Stock Award and set forth in the Award
Agreement, the effect of the Participant's termination of Service shall be as
follows: (a) the Company shall have the option to repurchase for the purchase
price paid by the Participant any shares acquired by the Participant pursuant to
a Restricted Stock Purchase Right which remain subject to Vesting Conditions as
of the date of the Participant's termination of Service and (b) the Participant
shall forfeit to the Company any shares acquired by the Participant pursuant to
a Restricted Stock Bonus which remain subject to


                                       13
<Page>


Vesting Conditions as of the date of the Participant's termination of Service.
The Company shall have the right to assign at any time any repurchase right or
reacquisition right it may have, whether or not such right is then exercisable,
to one or more persons as may be selected by the Company.

                  7.7      NONTRANSFERABILITY OF RESTRICTED STOCK AWARD RIGHTS.
Rights to acquire shares of Stock pursuant to a Restricted Stock Award may not
be assigned or transferred in any manner except by will or the laws of descent
and distribution, and, during the lifetime of the Participant, shall be
exercisable only by the Participant.

         8.       STANDARD FORMS OF AGREEMENT.

                  8.1      AGREEMENT. Unless otherwise provided by the Board at
the time the Award is granted, an Award shall comply with and be subject to the
terms and conditions set forth in the form of Award Agreement approved by the
Board and as amended from time to time.

                  8.2      AUTHORITY TO VARY TERMS. The Board shall have the
authority from time to time to vary the terms of any standard form of Award
Agreement described in this Section 8 either in connection with the grant or
amendment of an individual Award or in connection with the authorization of a
new standard form or forms; provided, however, that the terms and conditions of
any such new, revised or amended standard form or forms of Award Agreement are
not inconsistent with the terms of the Plan.

         9.       CHANGE IN CONTROL.

                  9.1      DEFINITIONS.

                           (a)      An "OWNERSHIP CHANGE EVENT" shall be deemed
to have occurred if any of the following occurs with respect to the Company: (i)
the direct or indirect sale or exchange in a single or series of related
transactions by the stockholders of the Company of more than fifty percent (50%)
of the voting stock of the Company; (ii) a merger or consolidation in which the
Company is a party; (iii) the sale, exchange, or transfer of all or
substantially all of the assets of the Company; or (iv) a liquidation or
dissolution of the Company.

                           (b)      A "CHANGE IN CONTROL" shall mean an
Ownership Change Event or a series of related Ownership Change Events
(collectively, a "TRANSACTION") wherein the stockholders of the Company
immediately before the Transaction do not retain immediately after the
Transaction, in substantially the same proportions as their ownership of shares
of the Company's voting stock immediately before the Transaction, direct or
indirect beneficial ownership of more than fifty percent (50%) of the total
combined voting power of the outstanding voting securities of the Company or, in
the case of a Transaction described in Section 9.1(a)(iii), the corporation or
other business entity to which the assets of the Company were transferred (the
"TRANSFEREE"), as the case may be. For purposes of the preceding sentence,
indirect beneficial ownership shall include, without limitation, an interest
resulting from ownership of the voting securities of one or more corporations or
other business entities which own the Company or the Transferee, as the case may
be, either directly or through one or


                                       14
<Page>


more subsidiary corporations or other business entities. The Board shall have
the right to determine whether multiple sales or exchanges of the voting
securities of the Company or multiple Ownership Change Events are related, and
its determination shall be final, binding and conclusive.

                  9.2      EFFECT OF CHANGE IN CONTROL ON OPTIONS.

                           (a)      ACCELERATED VESTING. Notwithstanding any
other provision of the Plan to the contrary, the Board, in its sole discretion,
may provide in any Option Agreement or, in the event of a Change in Control, may
take such actions as it deems appropriate to provide for the acceleration of the
exercisability and vesting in connection with such Change in Control of any or
all outstanding Options and shares acquired upon the exercise of such Options.

                           (b)      ASSUMPTION OR SUBSTITUTION OF OPTIONS. In
the event of a Change in Control, the surviving, continuing, successor, or
purchasing corporation or other business entity or parent corporation thereof,
as the case may be (the "ACQUIRING CORPORATION"), may either assume the
Company's rights and obligations under outstanding Options or substitute for
outstanding Options substantially equivalent options for the Acquiring
Corporation's stock. Any Options which are neither assumed or substituted for by
the Acquiring Corporation in connection with the Change in Control nor exercised
as of the date of the Change in Control shall terminate and cease to be
outstanding effective as of the date of the Change in Control. Notwithstanding
the foregoing, shares acquired upon exercise of an Option prior to the Change in
Control and any consideration received pursuant to the Change in Control with
respect to such shares shall continue to be subject to all applicable provisions
of the Option Agreement evidencing such Option except as otherwise provided in
such Option Agreement.

                           (c)      CASH-OUT OF OPTIONS. The Board may, in its
sole discretion and without the consent of any Optionee, determine that, upon
the occurrence of a Change in Control, each or any Option outstanding
immediately prior to the Change in Control shall be canceled in exchange for a
payment with respect to each vested share of Stock subject to such canceled
Option in (i) cash, (ii) stock of the Company or of a corporation or other
business entity a party to the Change in Control, or (iii) other property which,
in any such case, shall be in an amount having a Fair Market Value equal to the
Fair Market Value of the consideration to be paid per share of Stock in the
Change in Control over the exercise price per share under such Option (the
"SPREAD"). In the event such determination is made by the Board, the Spread
(reduced by applicable withholding taxes, if any) shall be paid to Optionees in
respect of their canceled Options as soon as practicable following the date of
the Change in Control.

                  9.3      EFFECT OF CHANGE IN CONTROL ON RESTRICTED STOCK
AWARDS. The Board may, in its discretion, provide in any Restricted Stock Award
Agreement that, in the event of a Change in Control, the lapsing of the Vesting
Conditions applicable to the shares subject to the Restricted Stock Award held
by a Participant whose Service has not terminated prior to such date shall be
accelerated effective as of the date of the Change in Control to such extent as
specified in such Award Agreement. Any acceleration of the lapsing of Vesting
Conditions that was permissible solely by reason of this Section 9.3 and the
provisions of such Award Agreement shall be conditioned upon the consummation of
the Change in Control.


                                       15

<Page>


         10.      PROVISION OF INFORMATION.

                  Each Participant shall be given access to information
concerning the Company equivalent to that information generally made available
to the Company's common stockholders.

         11.      COMPLIANCE WITH SECURITIES LAW.

                  The grant of Awards and the issuance of shares of Stock upon
exercise of Awards shall be subject to compliance with all applicable
requirements of federal, state and foreign law with respect to such securities.
Awards may not be exercised if the issuance of shares of Stock upon exercise
would constitute a violation of any applicable federal, state or foreign
securities laws or other law or regulations or the requirements of any stock
exchange or market system upon which the Stock may then be listed. In addition,
no Award may be exercised unless (a) a registration statement under the
Securities Act shall at the time of exercise of the Award be in effect with
respect to the shares issuable upon exercise of the Award or (b) in the opinion
of legal counsel to the Company, the shares issuable upon exercise of the Award
may be issued in accordance with the terms of an applicable exemption from the
registration requirements of the Securities Act. The inability of the Company to
obtain from any regulatory body having jurisdiction the authority, if any,
deemed by the Company's legal counsel to be necessary to the lawful issuance and
sale of any shares hereunder shall relieve the Company of any liability in
respect of the failure to issue or sell such shares as to which such requisite
authority shall not have been obtained. As a condition to the exercise of any
Award, the Company may require the Participant to satisfy any qualifications
that may be necessary or appropriate, to evidence compliance with any applicable
law or regulation and to make any representation or warranty with respect
thereto as may be requested by the Company.

         12.      TERMINATION OR AMENDMENT OF PLAN.

                  The Board may terminate or amend the Plan at any time.
However, subject to changes in applicable law, regulations or rules that would
permit otherwise, without the approval of the Company's stockholders, there
shall be (a) no increase in the maximum aggregate number of shares of Stock that
may be issued under the Plan (except by operation of the provisions of Section
4.2), (b) no change in the class of persons eligible to receive Incentive Stock
Options, and (c) no other amendment of the Plan that would require approval of
the Company's stockholders under any applicable law, regulation or rule. No
termination or amendment of the Plan shall affect any then outstanding Award
unless expressly provided by the Board. In any event, no termination or
amendment of the Plan may adversely affect any then outstanding Award without
the consent of the Participant, unless such termination or amendment is required
to enable an Option designated as an Incentive Stock Option to qualify as an
Incentive Stock Option or is necessary to comply with any applicable law,
regulation or rule.


                                       16
<Page>


                                  PLAN HISTORY


April 17, 2002             Board of Directors of MitoKor, a California
                           corporation ("MitoKor California") adopts Plan, with
                           an initial reserve of 1,500,000 shares, increased on
                           January 1, 2003 and each January 1 thereafter by a
                           number of shares equal to the lesser of (a) 4% of
                           the number of shares issued and outstanding on the
                           preceding December 31; or (b) such lesser number of
                           shares determined by the Board.

__________, 2002           Shareholders of MitoKor California approve Plan.

__________, 2002           Effective date of Delaware reincorporation of
                           MitoKor California.

__________, 2002           Effective date of the Plan.


<Page>


                                  MITOKOR, INC.
                             STOCK OPTION AGREEMENT


         MitoKor, Inc. has granted to the individual (the "OPTIONEE") named in
the NOTICE OF GRANT OF STOCK OPTIONS (the "NOTICE") to which this Stock Option
Agreement (the "OPTION AGREEMENT") is attached an option (the "OPTION") to
purchase certain shares of Stock upon the terms and conditions set forth in the
Notice and this Option Agreement. The Option has been granted pursuant to and
shall in all respects be subject to the terms and conditions of the MitoKor,
Inc. 2002 Stock Option Plan (the "PLAN"), as amended to the Date of Option
Grant, the provisions of which are incorporated herein by reference. By signing
the Notice, the Optionee: (a) represents that the Optionee has read and is
familiar with the terms and conditions of the Notice, the Plan and this Option
Agreement, including the Effect of Termination of Service set forth in Section
7, (b) accepts the Option subject to all of the terms and conditions of the
Notice, the Plan and this Option Agreement, (c) agrees to accept as binding,
conclusive and final all decisions or interpretations of the Board upon any
questions arising under the Notice, the Plan or this Option Agreement, and (d)
acknowledges receipt of a copy of the Notice, the Plan and this Option
Agreement.

         1.       DEFINITIONS AND CONSTRUCTION.

                  1.1      DEFINITIONS. Unless otherwise defined herein,
capitalized terms shall have the meanings assigned to such terms in the Notice
or the Plan. Whenever used herein, the following terms shall have their
respective meanings set forth below:

                           (a)      "DATE OF OPTION GRANT" means the effective
date of grant of the Option as set forth in the Notice.

                           (b)      "NUMBER OF OPTION SHARES" means the total
number of shares of Stock subject to the Option as set forth in the Notice and
as adjusted from time to time pursuant to Section 8.

                           (c)      "EXERCISE PRICE" means the purchase price
per share of Stock as set forth in the Notice and as adjusted from time to time
pursuant to Section 8.

                           (d)      "OPTION EXPIRATION DATE" means the date ten
(10) years after the Date of Option Grant.

                           (e)      "VESTED SHARES" means, on any relevant date,
that portion of the Number of Option Shares which has vested in accordance with
vesting schedule set forth in the Notice. Provided that the Optionee's Service
has not terminated prior to the relevant date, an initial installment of shares
will become Vested Shares on the initial "Full Vest" date set forth in the
Notice, and thereafter the remaining shares will become Vested Shares in
substantially equal installments at the periodic rate set forth in the Notice,
with the last such installment vesting on the last "Full Vest" date set forth in
the Notice.


                                       1
<Page>


                  1.2      CONSTRUCTION. Captions and titles contained herein
are for convenience only and shall not affect the meaning or interpretation of
any provision of this Option Agreement. Except when otherwise indicated by the
context, the singular shall include the plural and the plural shall include the
singular. Use of the term "or" is not intended to be exclusive, unless the
context clearly requires otherwise.

         2.       TAX CONSEQUENCES.

                  2.1      TAX STATUS OF OPTION. This Option is intended to have
the tax status designated in the Notice.

                           (a)      INCENTIVE STOCK OPTION. If the Notice so
designates, this Option is intended to be an Incentive Stock Option within the
meaning of Section 422(b) of the Code, but the Company does not represent or
warrant that this Option qualifies as such. The Optionee should consult with the
Optionee's own tax advisor regarding the tax effects of this Option and the
requirements necessary to obtain favorable income tax treatment under Section
422 of the Code, including, but not limited to, holding period requirements.
(NOTE TO OPTIONEE: If the Option is exercised more than three (3) months after
the date on which you cease to be an Employee (other than by reason of your
death or permanent and total disability as defined in Section 22(e)(3) of the
Code), the Option will be treated as a Nonstatutory Stock Option and not as an
Incentive Stock Option to the extent required by Section 422 of the Code.)

                           (b)      NONSTATUTORY STOCK OPTION. If the Notice so
designates, this Option is intended to be a Nonstatutory Stock Option and shall
not be treated as an Incentive Stock Option within the meaning of Section 422(b)
of the Code.

                  2.2      ISO FAIR MARKET VALUE LIMITATION. IF THE NOTICE
DESIGNATES THIS OPTION AS AN INCENTIVE STOCK OPTION, then to the extent that the
Option (together with all Incentive Stock Options granted to the Optionee under
all stock option plans of the Participating Company Group, including the Plan)
becomes exercisable for the first time during any calendar year for shares
having a Fair Market Value greater than One Hundred Thousand Dollars ($100,000),
the portion of such options which exceeds such amount will be treated as
Nonstatutory Stock Options. For purposes of this Section 2.2, options designated
as Incentive Stock Options are taken into account in the order in which they
were granted, and the Fair Market Value of stock is determined as of the time
the option with respect to such stock is granted. If the Code is amended to
provide for a different limitation from that set forth in this Section 2.2, such
different limitation shall be deemed incorporated herein effective as of the
date required or permitted by such amendment to the Code. If the Option is
treated as an Incentive Stock Option in part and as a Nonstatutory Stock Option
in part by reason of the limitation set forth in this Section 2.2, the Optionee
may designate which portion of such Option the Optionee is exercising. In the
absence of such designation, the Optionee shall be deemed to have exercised the
Incentive Stock Option portion of the Option first. Separate certificates
representing each such portion shall be issued upon the exercise of the Option.
(NOTE TO OPTIONEE: If the aggregate Exercise Price of the Option (that is, the
Exercise Price multiplied by the Number of Option Shares) plus the aggregate
exercise price of any other Incentive Stock Options you hold (whether granted
pursuant to the Plan or any other stock option plan of the Participating Company
Group) is greater than


                                       2
<Page>


$100,000, you should contact the Chief Financial Officer of the Company to
ascertain whether the entire Option qualifies as an Incentive Stock Option.)

         3.       ADMINISTRATION.

                  All questions of interpretation concerning this Option
Agreement shall be determined by the Board. All determinations by the Board
shall be final and binding upon all persons having an interest in the Option.
Any officer of a Participating Company shall have the authority to act on behalf
of the Company with respect to any matter, right, obligation, or election which
is the responsibility of or which is allocated to the Company herein, provided
the officer has apparent authority with respect to such matter, right,
obligation, or election.

         4.       EXERCISE OF THE OPTION.

                  4.1      RIGHT TO EXERCISE. Except as otherwise provided
herein, the Option shall be exercisable on and after the Date of Option Grant
and prior to the termination of the Option (as provided in Section 6) in an
amount not to exceed the number of Vested Shares less the number of shares
previously acquired upon exercise of the Option.

                  4.2      METHOD OF EXERCISE. Exercise of the Option shall be
by written notice to the Company which must state the election to exercise the
Option, the number of whole shares of Stock for which the Option is being
exercised and such other representations and agreements as to the Optionee's
investment intent with respect to such shares as may be required pursuant to the
provisions of this Option Agreement. The written notice must be signed by the
Optionee and must be delivered in person, by certified or registered mail,
return receipt requested, by confirmed facsimile transmission, or by such other
means as the Company may permit, to the Chief Financial Officer of the Company,
or other authorized representative of the Participating Company Group, prior to
the termination of the Option as set forth in Section 6, accompanied by full
payment of the aggregate Exercise Price for the number of shares of Stock being
purchased. The Option shall be deemed to be exercised upon receipt by the
Company of such written notice and the aggregate Exercise Price.

                  4.3      PAYMENT OF EXERCISE PRICE.

                           (a)      FORMS OF CONSIDERATION AUTHORIZED. Except as
otherwise provided below, payment of the aggregate Exercise Price for the number
of shares of Stock for which the Option is being exercised shall be made (i) in
cash, by check, or cash equivalent, (ii) by tender to the Company, or
attestation to the ownership, of whole shares of Stock owned by the Optionee
having a Fair Market Value (as determined by the Company without regard to any
restrictions on transferability applicable to such stock by reason of federal or
state securities laws or agreements with an underwriter for the Company) not
less than the aggregate Exercise Price, (iii) by means of a Cashless Exercise,
as defined in Section 4.3(b), or (iv) by any combination of the foregoing.

                           (b)      LIMITATIONS ON FORMS OF CONSIDERATION.

                                    (i)      TENDER OF STOCK. Notwithstanding
the foregoing, the Option may not be exercised by tender to the Company, or
attestation to the ownership, of shares


                                       3
<Page>


of Stock to the extent such tender or attestation would constitute a violation
of the provisions of any law, regulation or agreement restricting the redemption
of the Company's stock. The Option may not be exercised by tender to the
Company, or attestation to the ownership, of shares of Stock unless such shares
either have been owned by the Optionee for more than six (6) months or were not
acquired, directly or indirectly, from the Company.

                                    (ii)     CASHLESS EXERCISE. A "CASHLESS
EXERCISE" means the delivery of a properly executed notice together with
irrevocable instructions to a broker in a form acceptable to the Company
providing for the assignment to the Company of the proceeds of a sale or loan
with respect to some or all of the shares of Stock acquired upon the exercise of
the Option pursuant to a program or procedure approved by the Company
(including, without limitation, through an exercise complying with the
provisions of Regulation T as promulgated from time to time by the Board of
Governors of the Federal Reserve System). The Company reserves, at any and all
times, the right, in the Company's sole and absolute discretion, to decline to
approve or terminate any such program or procedure.

                  4.4      TAX WITHHOLDING. At the time the Option is exercised,
in whole or in part, or at any time thereafter as requested by the Company, the
Optionee hereby authorizes withholding from payroll and any other amounts
payable to the Optionee, and otherwise agrees to make adequate provision for
(including by means of a Cashless Exercise to the extent permitted by the
Company), any sums required to satisfy the federal, state, local and foreign tax
withholding obligations of the Participating Company Group, if any, which arise
in connection with the Option, including, without limitation, obligations
arising upon (i) the exercise, in whole or in part, of the Option, (ii) the
transfer, in whole or in part, of any shares acquired upon exercise of the
Option, (iii) the operation of any law or regulation providing for the
imputation of interest, or (iv) the lapsing of any restriction with respect to
any shares acquired upon exercise of the Option. The Company shall have no
obligation to deliver shares of Stock until the tax withholding obligations of
the Participating Company Group have been satisfied by the Optionee.

                  4.5      CERTIFICATE REGISTRATION. Except in the event the
Exercise Price is paid by means of a Cashless Exercise, the certificate for the
shares as to which the Option is exercised shall be registered in the name of
the Optionee, or, if applicable, in the names of the heirs of the Optionee.

                  4.6      RESTRICTIONS ON GRANT OF THE OPTION AND ISSUANCE OF
SHARES. The grant of the Option and the issuance of shares of Stock upon
exercise of the Option shall be subject to compliance with all applicable
requirements of federal, state or foreign law with respect to such securities.
The Option may not be exercised if the issuance of shares of Stock upon exercise
would constitute a violation of any applicable federal, state or foreign
securities laws or other law or regulations or the requirements of any stock
exchange or market system upon which the Stock may then be listed. In addition,
the Option may not be exercised unless (i) a registration statement under the
Securities Act shall at the time of exercise of the Option be in effect with
respect to the shares issuable upon exercise of the Option or (ii) in the
opinion of legal counsel to the Company, the shares issuable upon exercise of
the Option may be issued in accordance with the terms of an applicable exemption
from the registration requirements of the Securities Act. THE OPTIONEE IS
CAUTIONED THAT THE OPTION MAY NOT BE EXERCISED


                                       4
<Page>


UNLESS THE FOREGOING CONDITIONS ARE SATISFIED. ACCORDINGLY, THE OPTIONEE MAY NOT
BE ABLE TO EXERCISE THE OPTION WHEN DESIRED EVEN THOUGH THE OPTION IS VESTED.
The inability of the Company to obtain from any regulatory body having
jurisdiction the authority, if any, deemed by the Company's legal counsel to be
necessary to the lawful issuance and sale of any shares subject to the Option
shall relieve the Company of any liability in respect of the failure to issue or
sell such shares as to which such requisite authority shall not have been
obtained. As a condition to the exercise of the Option, the Company may require
the Optionee to satisfy any qualifications that may be necessary or appropriate,
to evidence compliance with any applicable law or regulation and to make any
representation or warranty with respect thereto as may be requested by the
Company.

                  4.7      FRACTIONAL SHARES. The Company shall not be required
to issue fractional shares upon the exercise of the Option.

         5.       NONTRANSFERABILITY OF THE OPTION.

                  The Option may be exercised during the lifetime of the
Optionee only by the Optionee or the Optionee's guardian or legal representative
and may not be assigned or transferred in any manner except by will or by the
laws of descent and distribution. Following the death of the Optionee, the
Option, to the extent provided in Section 7, may be exercised by the Optionee's
legal representative or by any person empowered to do so under the deceased
Optionee's will or under the then applicable laws of descent and distribution.

         6.       TERMINATION OF THE OPTION.

                  The Option shall terminate and may no longer be exercised on
the first to occur of (a) the Option Expiration Date, (b) the last date for
exercising the Option following termination of the Optionee's Service as
described in Section 7, or (c) a Change in Control to the extent provided in the
Plan.

         7.       EFFECT OF TERMINATION OF SERVICE.

                  7.1      OPTION EXERCISABILITY.

                           (a)      DISABILITY. If the Optionee's Service with
the Participating Company Group terminates because of the Disability of the
Optionee, the Option, to the extent unexercised and exercisable on the date on
which the Optionee's Service terminated, may be exercised by the Optionee (or
the Optionee's guardian or legal representative) at any time prior to the
expiration of one (1) year after the date on which the Optionee's Service
terminated, but in any event no later than the Option Expiration Date.

                           (b)      DEATH. If the Optionee's Service with the
Participating Company Group terminates because of the death of the Optionee, the
Option, to the extent unexercised and exercisable on the date on which the
Optionee's Service terminated, may be exercised by the Optionee's legal
representative or other person who acquired the right to exercise the Option by
reason of the Optionee's death at any time prior to the expiration of one (1)
year after the date on which the Optionee's Service terminated, but in any event
no later than the Option Expiration


                                       5
<Page>


Date. The Optionee's Service shall be deemed to have terminated on account of
death if the Optionee dies within ninety (90) days after the Optionee's
termination of Service.

                           (c)      OTHER TERMINATION OF SERVICE. If the
Optionee's Service with the Participating Company Group terminates for any
reason, except Disability or death, the Option, to the extent unexercised and
exercisable by the Optionee on the date on which the Optionee's Service
terminated, may be exercised by the Optionee at any time prior to the expiration
of ninety (90) days (or such other longer period of time as determined by the
Board, in its discretion) after the date on which the Optionee's Service
terminated, but in any event no later than the Option Expiration Date.

                  7.2      EXTENSION IF EXERCISE PREVENTED BY LAW.
Notwithstanding the foregoing, if the exercise of the Option within the
applicable time periods set forth in Section 7.1 is prevented by the provisions
of Section 4.6, the Option shall remain exercisable until three (3) months after
the date the Optionee is notified by the Company that the Option is exercisable,
but in any event no later than the Option Expiration Date.

                  7.3      EXTENSION IF OPTIONEE SUBJECT TO SECTION 16(b).
Notwithstanding the foregoing, if a sale within the applicable time periods set
forth in Section 7.1 of shares acquired upon the exercise of the Option would
subject the Optionee to suit under Section 16(b) of the Exchange Act, the Option
shall remain exercisable until the earliest to occur of (i) the tenth (10th) day
following the date on which a sale of such shares by the Optionee would no
longer be subject to such suit, (ii) the one hundred and ninetieth (190th) day
after the Optionee's termination of Service, or (iii) the Option Expiration
Date.

         8.       ADJUSTMENTS FOR CHANGES IN CAPITAL STRUCTURE.

                  In the event of any stock dividend, stock split, reverse stock
split, recapitalization, combination, reclassification, or similar change in the
capital structure of the Company, appropriate adjustments shall be made in the
number, Exercise Price and class of shares of stock subject to the Option. If a
majority of the shares which are of the same class as the shares that are
subject to the Option are exchanged for, converted into, or otherwise become
(whether or not pursuant to an Ownership Change Event) shares of another
corporation (the "NEW SHARES"), the Board may unilaterally amend the Option to
provide that the Option is exercisable for New Shares. In the event of any such
amendment, the Number of Option Shares and the Exercise Price shall be adjusted
in a fair and equitable manner, as determined by the Board, in its discretion.
Notwithstanding the foregoing, any fractional share resulting from an adjustment
pursuant to this Section 8 shall be rounded down to the nearest whole number,
and in no event may the Exercise Price be decreased to an amount less than the
par value, if any, of the stock subject to the Option. The adjustments
determined by the Board pursuant to this Section 8 shall be final, binding and
conclusive.

         9.       RIGHTS AS A STOCKHOLDER, EMPLOYEE OR CONSULTANT.

                  The Optionee shall have no rights as a stockholder with
respect to any shares covered by the Option until the date of the issuance of a
certificate for the shares for which the Option has been exercised (as evidenced
by the appropriate entry on the books of the Company


                                       6
<Page>


or of a duly authorized transfer agent of the Company). No adjustment shall be
made for dividends, distributions or other rights for which the record date is
prior to the date such certificate is issued, except as provided in Section 8.
If the Optionee is an Employee, the Optionee understands and acknowledges that,
except as otherwise provided in a separate, written employment agreement between
a Participating Company and the Optionee, the Optionee's employment is "at will"
and is for no specified term. Nothing in this Option Agreement shall confer upon
the Optionee any right to continue in the Service of a Participating Company or
interfere in any way with any right of the Participating Company Group to
terminate the Optionee's Service as an Employee or Consultant, as the case may
be, at any time.

         10.      NOTICE OF SALES UPON DISQUALIFYING DISPOSITION.

                  The Optionee shall dispose of the shares acquired pursuant to
the Option only in accordance with the provisions of this Option Agreement. In
addition, IF THE NOTICE DESIGNATES THIS OPTION AS AN INCENTIVE STOCK OPTION, the
Optionee shall (a) promptly notify the Chief Financial Officer of the Company if
the Optionee disposes of any of the shares acquired pursuant to the Option
within one (1) year after the date the Optionee exercises all or part of the
Option or within two (2) years after the Date of Option Grant and (b) provide
the Company with a description of the circumstances of such disposition. Until
such time as the Optionee disposes of such shares in a manner consistent with
the provisions of this Option Agreement, unless otherwise expressly authorized
by the Company, the Optionee shall hold all shares acquired pursuant to the
Option in the Optionee's name (and not in the name of any nominee) for the
one-year period immediately after the exercise of the Option and the two-year
period immediately after Date of Option Grant. At any time during the one-year
or two-year periods set forth above, the Company may place a legend on any
certificate representing shares acquired pursuant to the Option requesting the
transfer agent for the Company's stock to notify the Company of any such
transfers. The obligation of the Optionee to notify the Company of any such
transfer shall continue notwithstanding that a legend has been placed on the
certificate pursuant to the preceding sentence.

         11.      LEGENDS.

                  The Company may at any time place legends referencing any
applicable federal, state or foreign securities law restrictions, and, if
applicable, that the shares were acquired upon exercise of an Incentive Stock
Option, on all certificates representing shares of stock subject to the
provisions of this Option Agreement. The Optionee shall, at the request of the
Company, promptly present to the Company any and all certificates representing
shares acquired pursuant to the Option in the possession of the Optionee in
order to carry out the provisions of this Section.

         12.      MISCELLANEOUS PROVISIONS.

                  12.1     BINDING EFFECT. Subject to the restrictions on
transfer set forth herein, this Option Agreement shall inure to the benefit of
and be binding upon the parties hereto and their respective heirs, executors,
administrators, successors and assigns.


                                       7
<Page>


                  12.2     TERMINATION OR AMENDMENT. The Board may terminate or
amend the Plan or the Option at any time; provided, however, that except as
provided in the Plan in connection with a Change in Control, no such termination
or amendment may adversely affect the Option or any unexercised portion hereof
without the consent of the Optionee unless such termination or amendment is
necessary to comply with any applicable law or government regulation or is
required to enable the Option, if designated an Incentive Stock Option in the
Notice, to qualify as an Incentive Stock Option. No amendment or addition to
this Option Agreement shall be effective unless in writing.

                  12.3     NOTICES. Any notice required or permitted hereunder
shall be given in writing and shall be deemed effectively given (except to the
extent that this Option Agreement provides for effectiveness only upon actual
receipt of such notice) upon personal delivery or upon deposit in the United
States Post Office, by registered or certified mail, with postage and fees
prepaid, addressed to the other party at the address shown on the Notice or at
such other address as such party may designate in writing from time to time to
the other party.

                  12.4     INTEGRATED AGREEMENT. The Notice, this Option
Agreement and the Plan constitute the entire understanding and agreement of the
Optionee and the Participating Company Group with respect to the subject matter
contained herein or therein and supersedes any prior agreements, understandings,
restrictions, representations, or warranties among the Optionee and the
Participating Company Group with respect to such subject matter other than those
as set forth or provided for herein or therein. To the extent contemplated
herein or therein, the provisions of the Notice and the Option Agreement shall
survive any exercise of the Option and shall remain in full force and effect.

                  12.5     APPLICABLE LAW. This Option Agreement shall be
governed by the laws of the State of California as such laws are applied to
agreements between California residents entered into and to be performed
entirely within the State of California.

                  12.6     COUNTERPARTS. The Notice may be executed in
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.


                                       8

<Page>



/ /  Incentive Stock Option               Optionee:
                                                   -----------------------------
/ /  Nonstatutory Stock Option
                                          Date:
                                               ---------------------------------


                          STOCK OPTION EXERCISE NOTICE
                               (REGISTERED SHARES)


MitoKor, Inc.
Attention: Chief Financial Officer
11494 Sorrento Valley Road
San Diego, CA  92121

Ladies and Gentlemen:

         1.       OPTION. I was granted an option (the "OPTION") to purchase
shares of the common stock (the "SHARES") of MitoKor, Inc. (the "COMPANY")
pursuant to the Company's 2002 Stock Option Plan (the "PLAN"), my Notice of
Grant of Stock Options (the "NOTICE") and my Stock Option Agreement (the "OPTION
AGREEMENT") as follows:

                  Grant Number:
                                                    ----------------------------

                  Date of Option Grant:
                                                    ----------------------------

                  Number of Option Shares:
                                                    ----------------------------

                  Exercise Price per Share:         $
                                                     ---------------------------

         2.       EXERCISE OF OPTION. I hereby elect to exercise the Option to
purchase the following number of Shares:

                  Total Shares Purchased:
                                                    ----------------------------

                  Total Exercise Price (Total
                  Shares  X  Price per Share)       $
                                                     ---------------------------

         3.       PAYMENTS. I enclose payment in full of the total exercise
price for the Shares in the following form(s), as authorized by my Option
Agreement:

                  / /  Cash:                        $
                                                     ---------------------------

                  / /  Check:                       $
                                                     ---------------------------

                  / /  Tender of Company Stock:     Contact Plan Administrator

                  / /  Cashless exercise            Contact Plan Administrator

         4.       TAX WITHHOLDING. Subject to the Option Agreement, I authorize
payroll withholding and otherwise will make adequate provision for the federal,
state, local and foreign tax withholding obligations of the Company, if any, in
connection with the Option.


                                       1
<Page>


         5.       OPTIONEE INFORMATION.

                  My address is:
                                 -----------------------------------------------

                                 -----------------------------------------------

                  My Social Security Number is:
                                                --------------------------------

         6.       NOTICE OF DISQUALIFYING DISPOSITION. If the Option is an
Incentive Stock Option, I agree that I will promptly notify the Chief Financial
Officer of the Company if I transfer any of the Shares within one (1) year from
the date I exercise all or part of the Option or within two (2) years of the
Date of Option Grant.

         7.       BINDING EFFECT. I agree that the Shares are being acquired in
accordance with and subject to the terms, provisions and conditions of the
Option Agreement, to all of which I hereby expressly assent. This Agreement
shall inure to the benefit of and be binding upon the my heirs, executors,
administrators, successors and assigns.

         I understand that I am purchasing the Shares pursuant to the terms of
the Plan, the Notice and my Option Agreement, copies of which I have received
and carefully read and understand.

                                                  Very truly yours,


                                                  ------------------------------
                                                  (Signature)


Receipt of the above is hereby acknowledged.

MITOKOR, INC.

By:
     --------------------------------

Title:
        -----------------------------

Dated:
        -----------------------------


                                       2
<Page>


                                  MITOKOR, INC.
                         NOTICE OF GRANT OF STOCK OPTION

         ________________________ (the "OPTIONEE") has been granted an option
(the "OPTION") to purchase certain shares of Stock of MitoKor, Inc. pursuant to
the MitoKor, Inc. 2002 Stock Option Plan (the "PLAN"), as follows:

         DATE OF OPTION GRANT:      __________

         NUMBER OF OPTION SHARES:   __________

         EXERCISE PRICE:            $_________  per share

         INITIAL VESTING DATE:      The date one (1) year after  _______

         OPTION EXPIRATION DATE:    The date ten (10) years after the Date of
                                    Option Grant.

         TAX STATUS OF OPTION:      _____________ Stock Option. (Enter
                                    "Incentive" or "Nonstatutory." If blank,
                                    this Option will be a Nonstatutory Stock
                                    Option.)

         VESTED SHARES: Except as provided in the Stock Option Agreement, the
         number of Vested Shares (disregarding any resulting fractional share)
         as of any date is determined by multiplying the Number of Option Shares
         by the "VESTED RATIO" determined as of such date as follows:

<Table>
<Caption>

                                                                               Vested Ratio
                                                                               ------------
                                   <S>                                         <C>
                                   Prior to Initial Vesting Date                    0
                                   On Initial Vesting Date, provided the
                                   Optionee's Service has not
                                   terminated prior to such date                   1/5
                                   PLUS:
                                   For each three months of the
                                   Optionee's continuous Service from
                                   Initial Vesting Date until the
                                   Vested Ratio equals 1/1, an
                                   additional                                     1/20

</Table>

         By their signatures below, the Company and the Optionee agree that the
Option is governed by this Notice and by the provisions of the Plan and the
Stock Option Agreement, both of which are attached to and made a part of this
document. The Optionee acknowledges receipt of copies of the Plan and the Stock
Option Agreement, represents that the Optionee has read and is familiar with
their provisions, and hereby accepts the Option subject to all of their terms
and conditions.

MITOKOR, INC.                                        OPTIONEE

By:
    ---------------------------------         ----------------------------------
                                              Signature
Its:
     --------------------------------         ----------------------------------
                                              Date

Address: 11494 Sorrento Valley Road
         San Diego, CA  92121                 ----------------------------------
                                              Address

                                              ----------------------------------

ATTACHMENTS:      2002 Stock Option Plan, as amended to the Date of Option
                  Grant; Stock Option Agreement and Exercise Notice