gavin <gavin at zonvark.wustl.edu> wrote in message news:<3BC0E343.192978FB at zonvark.wustl.edu>...
> It's true that kinetics is important in biochemical reactions.
> But the reaction must first have the
> thermodynamic drive to proceed. If the Gibbs free energy
> is positive (i.e. unfavorable going from
> left to right), there is no amount of rate constant that can make
> the reaction to go from left to right.
That is true, but the phenomenon of "kinetic control" vs.
"thermodynamic control" is more subtle. At issue is not a particular
processes (biochemical reaction) taken in isolation, which is what you
are referring to.
Instead, consider two biochemical processes proceeding at the same
time:
A ---> B1 : dG1
A ---> B2 : dG2
It is possible that dG2 is more negative then dG1, which means at
thermodynamic equilibrium you would expect more B2 than B1.
Despite of this fact, under "kinetic control" (determined by the
values of rate constants) the product B1 might be formed in
significantly greater amount in comparison with B2.
In this sense, thermodynamic considerations are misleading, not
applicable to understanding what might happen in the cell. This
seems to be the case with zinc trafficking.
- Petr
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