Evolution of enzyme catalytic power. Characteristics of optimal catalysis evaluated for the simplest plausible kinetic model

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Abstract
Evolutionary changes in the structure of an enzyme that provide an increase in its Km value are considered. Provided that Km increases as a result of increases in the forward rate constants of the catalysis relative to the reverse rate constants, the enzyme catalyzes the conversion of a fixed concentration of its substrate [S] more rapidly when its structure provides that Km > [S] than when Km < [S]. Catalytic efficiency of enzymes is discussed in terms of the simplest plausible model, the Haldane reversible 3-step model. The existing literature suggests that, in general, appropriate values of Km have evolved for the provision of high rates of catalysis but that many values of kcat catalytic constant are not large enough to provide optimal rates of catalysis unless the value of k+1 in vivo is lower than its value in free solution.