Michael Kohn wrote:
>Knowles showed that the
>rate constants for the bimolecular steps in the TPI catalytic cycle were well
>matched to the rates of diffusion of substrates to the active site. That is,
>the enzyme had evolved to a state of "perfection" (Knowles' term) as the
>reaction could not be catalyzed to occur any faster, being limited by
>diffusion.
Just a note to say that the Albery and Knowles concept of
catalytic perfection is far from straight forward. There could
be many other definitions of catalytic perfection or efficiency.
We analysed the control coefficients of the rate constants and
steps within TPI (triose phosphate isomerase) using Albery and
Knowles own data, and showed that even with low substrate and
zero product, there was a significant amount of control over
the enzyme's rate by steps internal to the enzyme (i.e. not
diffusion or substrate binding). Thus the enzyme certainly
could evolve to go faster by increasing the rate constants
of the catlytic steps, thus it was not catalytically perfect
even by their own criteria. Brown & Cooper (1993) Control
analysis applied to single enzymes: can an isolated enzyme
have a unique rate-limiting step? Biochem Journal 294, 87-94.
Guy Brown
Dr Guy C. Brown
Department of Biochemistry,
University of Cambridge,
Tennis Court Road,
Cambridge CB2 1QW, UK.
Tel: (44) (0)1223 333342
Fax: (44) (0)1223 333345
e-mail: gcb at mole.bio.cam.ac.ukhttp://www.bio.cam.ac.uk/dept/biochem/brown/index.html
