You could make use of product binding energy to drive the
reaction forward while the substrate/product is bound to the
enzyme. But enzymes that pull that trick are barely
"enzymes" - they stay stuck to the first product they make
until something else uses some energy to release it.
You can't change the equilibrium constant of the overall
reaction - that would violate basic thermodynamics.
This sounds a lot like a homework question I would assign my
undergrads!
Phoebe
---- Original message ----
>Date: Tue, 18 May 2010 09:39:49 -0600
>From: Maia Cherney <[log in to unmask]>
>Subject: Re: [ccp4bb] Is it possible to mutate a reversible
epimerase into an inreversible one?
>To: [log in to unmask]
>
>I think that it's possible to do a mutation that affects only
one way of
>the reaction. You can mutate a residue that makes contacts
only with the
>product of the direct way or only of the reverse way.
>
>Maia
>
>Randy Read wrote:
>> Dear Vinson,
>>
>> I would agree with you on choice B. There are probably
many ways to
>> look at it. Here are two that come to me at the moment.
>>
>> 1. If the reaction is reversible, then there's no
opportunity to put
>> energy into the system to reduce its overall entropy. So a
reversible
>> epimerase would be like a Maxwell's demon, violating the
second law of
>> thermodynamics.
>>
>> 2. Reversible reactions obey the principle of microscopic
>> reversibility, i.e. the reaction mechanism and the
transition states
>> are the same in both directions. There's no way for an
enzyme to
>> selectively reduce the transition state barrier going in
one direction
>> but not the other.
>>
>> Regards,
>>
>> Randy Read
>>
>> On 18 May 2010, at 08:31, Vinson LIANG wrote:
>>
>>> Dear all,
>>>
>>> Sorry for this silly biochemistory question. Thing is
that I have a
>>> reversible epimerase and I want to mutate it into an
inreversible
>>> one. However, I have been told that the ΔG of a reversible
reaction
>>> is zero. Which direction the reaction goes depends only on
the
>>> concentration of the substrate. So the conclusion is,
>>>
>>> A: I can mutate the epimerase into an inreversible one.
But it has no
>>> influence on the reaction direction, and hence it has
little mean.
>>>
>>> B: There is no way to change a reversible epimerase into an
>>> inversible one.
>>>
>>> Could somebody please give me some comment on the two
conclution?
>>>
>>> Thank you all for your time.
>>>
>>> Best,
>>>
>>> Vinson
>>>
>>>
>>>
>>
>> ------
>> Randy J. Read
>> Department of Haematology, University of Cambridge
>> Cambridge Institute for Medical Research Tel: + 44
1223 336500
>> Wellcome Trust/MRC Building Fax: + 44
1223 336827
>> Hills Road E-mail:
[log in to unmask]
>> <mailto:[log in to unmask]>
>> Cambridge CB2 0XY, U.K.
www-structmed.cimr.cam.ac.uk
>>
Phoebe A. Rice
Assoc. Prof., Dept. of Biochemistry & Molecular Biology
The University of Chicago
phone 773 834 1723
http://bmb.bsd.uchicago.edu/Faculty_and_Research/01_Faculty/01_Faculty_Alphabetically.php?faculty_id=123
RNA is really nifty
DNA is over fifty
We have put them
both in one book
Please do take a
really good look
http://www.rsc.org/shop/books/2008/9780854042722.asp
|