You absolutely right, I thought about it.
Maia
Marius Schmidt wrote:
> Interestingly, Maxwell's demon pops up here, whoooo... ,
> don't do it.
>
>
>
>
>> If you change the reaction rate in one direction 1000 times slower
>> than
>> in the other direction, then the reaction becomes practically
>> irreversible. And the system might not be at equilibrium.
>>
>> Maia
>>
>> R. M. Garavito wrote:
>>
>>> Vinson,
>>>
>>> As Dale and Randy pointed out, you cannot change the ΔG of a reaction
>>> by mutation: enzyme, which is a catalyst, affects only the activation
>>> barrier (ΔE "double-dagger"). You can just make it a better (or
>>> worse) catalyst which would allow the reaction to flow faster (or
>>> slower) towards equilibrium. Nature solves this problem very
>>> elegantly by taking a readily reversible enzyme, like an epimerase or
>>> isomerase, and coupling it to a much less reversible reaction which
>>> removes product quickly. Hence, the mass action is only in one
>>> direction. An example of such an arrangement is the triose phosphate
>>> isomerase (TIM)-glyceraldehyde 3-phosphate dehydrogenase (GAPDH)
>>> reaction pair. TIM is readily reversible (DHA <=> G3P), but G3P is
>>> rapidly converted to 1,3-diphosphoglycerate by GAPDH. The oxidation
>>> and phosphorylation reactions of GAPDH now make TIM "work" in one
>>> direction.
>>>
>>> Since many epimerases are very optimized enzymes, why not consider
>>> making a fusion with a second enzyme (like a reductase) to make the
>>> system flow in one direction. Of course, this depends on what you
>>> want to do with the product.
>>>
>>> Cheers,
>>>
>>> Michael
>>>
>>> /****************************************************************/
>>> /R. Michael Garavito, Ph.D./
>>> /Professor of Biochemistry & Molecular Biology/
>>> /513 Biochemistry Bldg. /
>>> /Michigan State University /
>>> /East Lansing, MI 48824-1319/
>>> /Office:// //(517) 355-9724 Lab: (517) 353-9125/
>>> /FAX: (517) 353-9334 Email: [log in to unmask]
>>> <mailto:[log in to unmask]>/
>>> /****************************************************************/
>>>
>>>
>>>
>>> On May 18, 2010, at 11:54 AM, Dale Tronrud wrote:
>>>
>>>
>>>> Hi,
>>>>
>>>> I'm more of a Fourier coefficient kind of guy, but I thought that a
>>>> ΔG of zero simply corresponded to an equilibrium constant of one. You
>>>> can certainly have reversible reactions with other equilibrium constants.
>>>> In fact I think "irreversible" reactions are simply ones where the
>>>> equilibrium constant is so far to one side that, in practice, the
>>>> reaction
>>>> always goes all the way to product.
>>>>
>>>> As Randy pointed out the enzyme cannot change the ΔG (or the
>>>> equilibrium
>>>> constant). You could drive a reaction out of equilibrium by coupling it
>>>> to some other reaction which itself is way out of equilibrium (such as
>>>> ATP hydrolysis in the cell) but I don't think that's a simple mutation of
>>>> your enzyme. ;-)
>>>>
>>>> Dale Tronrud
>>>>
>>>> On 05/18/10 00:31, 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
>>>>>
>>>>>
>>>>>
>>>>>
>
> Dr.habil. Marius Schmidt
> Asst. Professor
> University of Wisconsin-Milwaukee
> Department of Physics Room 454
> 1900 E. Kenwood Blvd.
> Milwaukee, WI 53211
>
> phone: +1-414-229-4338
> email: [log in to unmask]
> http://users.physik.tu-muenchen.de/marius/
>
>
>
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