The Theory of Alternative Substrates in Enzyme Kinetics and Its Application to Yeast Hexokinase

Abstract

The theory of alternative substrates has been thoroughly investigated. The reciprocal rate equations, for ordered and random kinetic mechanisms, in the presence of an alternative substrate, have been developed. The conditions in which those equations give rise to either hyperbolic or linear reciprocal plots have been established. Degeneracy and constraint conditions of the various kinetic models have also been derived. Definite conclusions concerning the relevant mechanism can be obtained only if the Dalziel coefficients pertaining to the substrate are different from those corresponding to the alternative substrate. It follows from this, that the method termed “isotope competition”, cannot be used to make a choice among various two‐substrate mechanisms, and appears to be unfounded. The theory of alternative substrates has been applied to the study of yeast hexokinase. The results obtained are at variance with a random mechanism. They do agree, on the other hand, with a compulsory order of substrate binding on the enzyme, glucose being bound first.