Athel Cornish-Bowden wrote:
> > [...] Can we expect that the rate constants
> >change proportionally so that their ratio K = Kf/Kb remains the same?
>> Yes, we must expect it: if the kinetics don't agree with thermodynamic
> necessity there is something wrong with the kinetic model.
Perhaps a semantic footnote might be appropriate here. I submit that
the rate constants k+ and k- in
k+
A + B <==> C /1/
k-
do not "change" at all merely upon adding a catalyst, which causes an
entirely different sequence of steps to occur, for example (in the case
of an enzyme following the ordered 'bi-uni' mechanism)
k1
A + E <==> EA /2/
k2
k3
EA + B <==> EAB /3/
k4
k5
EAB <==> EC /4/
k6
k7
EC <==> E + C /5/
k8
so that the complete reaction mechanism now consists of reactions /1/ -
/5/.
The rate constants k+, k- that describe the uncatalyzed process (true to
their designation as 'constants') can change only with temperature,
pressure, or other physical factors, but not by the presence of a
catalyst.
Petr
_____________________________________________________________
Petr Kuzmic Ph.D. * BioKin Ltd. * Madison, WI 53708-8336, USA
pkuzmic at biokin.com * http://www.biokin.com * 608.256.1269 fax
