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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 >