[Description of the kinetics of the two substrate reactions S1+S2 goes to and comes from S3+S4 by a generalized Monod, Wyman, Changeux model].

A number of mathematical models, generalizations of the Monod, Wyman, Changeux model, have been derived describing the kinetics of two substrate reactions S1+S2 (formula: see text) S3+S4. Protomers of the olygomeric enzyme E(R, T) undergo concerted conformational transitions of the type R in equilibrium T. Cases of ordered and random substrate and product binding to the active sites of the enzyme have been considered. The models have been shown to account for the isosteric substrate activation (sigmoidal curves upsilon (S1) and upsilon(S2) and substrate inhibition of the enzyme as well as activation by one substrate and inhibition by the other. Products can exert both activating and inhibiting isosteric effects on the enzyme. Relative advantages of the two main methods of parameter estimation, experimental-kinetic and mathematical, have been discussed. The second method has been illustrated by fitting one of the models to experimental data for substrate saturation of human platelet phosphofructokinase.