A new approach for determination of the selectively favoured kinetic design of enzyme reactions

A new criterion is applied for characterization of the kinetic design of enzymes that should be favoured by a selective pressure in the direction of increased metabolic reaction flux. According to this criterion, the selectively favoured state of a metabolic sequence of enzyme reactions conforming to Michaelis-Menten kinetics is identical with the uniform one which is known to optimize reaction flux for a given average magnitude of enzyme concentrations and of true and apparent first-order rate constants in the reaction system. It is argued that presently observed values of on-velocity constants for metabolite binding to enzymes are unlikely to represent the upper limit for a diffusion-controlled association process and are more likely to represent those corresponding to the selectively favoured kinetic design at the present stage of the evolutionary development of enzyme function. (C) 1996 Academic Press Limited