I am a rank beginner here, but having just read Kacser and Burns (Symp
Soc Exp Biol 27:65-104, 1973) for the first time I am surprised by some
of the responses in this thread.
I gather everyone agrees that quasi-equilibrium steps make poor control
points, but proving this is said to be another matter. For example,
Athel says that in practice close-to-equilibrium reactions have
small-to-negligible flux control coefficients, but that Kacser always
argued that one has no justification for assuming that quasi-equilibrium
steps have very low flux-control coefficients.
I probably don't yet completely understand the terminology, but if a
flux control coefficient is the same as Kacser's Sensitivity
coefficient, Z, or even if it's the same as his response, R, (=Z*kappa),
then it seems to me Kacser, himself, provided the required proof.
Kacser shows that the ratios of the Zi for a sequential series of
reactions can be written as functions of the Vmi, the Kmi, and the Keqi
(When will we get subscripts on the net? :-) and that these ratios can
be rearranged in the form Z1:Z2:Z3 :: 1-p1:p1(1-p2):p1p2(1-p3), where
the pi (rho-sub-i) are the mass-action ratios for each step divided by
the equilibrium constant for that step.
This means, as Kacser is quick to point out, that for any step close to
equilibrium, pi will be nearly 1 and the corresponding Z will be zero.
Since R=kappa*Z, this is true of R as well.
So I'm not sure how to translate this into the current terminology, but
I have a strong feeling that this is closely related to the initial
question in this thread.
I've only been part of this newsgroup for a short while, but I already
feel I should have been here years ago. Perhaps someone will educate me
still further, but I found Kacser eye-opening and profound.
Can anyone tell me something about the intellectual lineage of people
working in this field today? You all seem to know each other well; did
you all train in the same labs? Thanks.
Regards,
Bob
--
Robert D. Phair, Ph.D. rphair at ix.netcom.com
BioInformatics Services http://www.webcom.com/rphair
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