Petr Kuzmic wrote:>>>>>>>>>>>>>>
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.<<<<<<<<<<<<<<<<<<<<<
Of course. If k8(E) >> k- (E is the enzyme concentration), we can neglect
the uncatalyzed process but still the ratio k8(E)/k- remains crucial. Let us
try to determine the substitute for k+ for the catalyzed process: if it is
k+_catalyzed, we can reformulate the second law in kinetic terms:
(k+_catalyzed)/(k+) = (k8)(E)/(k-) /6/
I am not sure that /6/ is unproblematic.
Best regards,
Pentcho
