On 14 May 98 at 11:43, Johann M. Rohwer wrote:
> And there are cases where we feel that calling something a control
> coefficient after changing an enzyme concentration (e.g., in group
> transfer pathways) is wrong. Again, these will most probably be the
> minority of cases, but that does not detract from the need for a sound
> general definition.
I would say that these will most probably be the majority of cases for
_in_vivo_ experiments. But then this lends even more support for the
need of a general (and CORRECT) definition of control coefficients.
In my opinion this point in your paper is simply a clarification. As I
said in the 1996 BTK meeting, Kacser & Burns' 1973 paper already defines
control coefficient in terms of rates of reaction. That many subsequent
papers by other MCA authors deny this is IMHO one of the major blunders of
the field. It led to some MCA opponents to state that MCA is not applicable
to "non-ideal" reactions when truly speaking it always did. This emphasises
the need for a clarification that the paper under discussion does very well
indeed.
With respect to the cases when rate of reaction is not linear in terms of
enzyme concentration and/or independent of other enzyme concentrations. I
would say that the "level of aggregation suitable" (as Johann put it) can
be either
(1) the reductionist elementary mechanistic level
(2) the "wholistic" higher level of a group of enzymes (eg Paul Srere's
metabolon) that are not kinetically independent
(2) follows Henrik Kacser's spirit of a descritption that does not require
knowledge of mechanism, while (1) does not. It is interesting that so far
(2) has not been much used for such systems.
Pedro
Pedro Mendes Inst. Biological Sciences
prm at aber.ac.uk (home: pedro at enzyme.demon.co.uk) Univ. Wales, Aberystwyth,
http://gepasi.dbs.aber.ac.uk/pedro/prmhome.htm Ceredigion SY23 3DD, U.K.
http://gepasi.dbs.aber.ac.uk/softw/gepasi.html FAX: +44 (0)1970 622307
