Kinetics of competitive binding with application to thrombin complexes

Abstract

The kinetics of competitive binding is treated analytically, allowing the rate constants to be determined accurately from simple experiments. The method is especially suited to situations where traditional approximations and numerical integration fail, e.g., when the dissociation constants are small or when the concentration of one receptor cannot be measured accurately. The method is applied to the competitive binding of hirudin to thrombin and anhydrothrombin and found to be accurate to a few parts in ten million. The fitted rate constants show that anhydrothrombin binds hirudin more weakly than thrombin, with a 2.6-fold increase in its dissociation constant. The small relative difference in binding free energy (0.6 kcal/mol) indicates that anhydrothrombin is structurally similar to thrombin.