Kinetics of complex formation of molybdate with 8-hydroxyquinoline. A model system for enzyme-substrate binding in xanthine oxidase

Abstract

Using the temperature-jumps relaxation technique the kinetics of complex formation between molybdate and 8-hydroxyquinoline have been studied in the pH range 7.9–8.9. A reaction scheme for formation of the 1:1 complex is proposed which accounts for the observed pH dependence of the overall forward and backward rate constants. The specific rate constants evaluated are discussed in terms of the detailed reaction mechanism. Complex formation between molybdate and 8-hydroxyquinoline may be regarded as a model for the binding of substrate by the enzyme xanthine oxidase. This enzyme contains molybdenum which probably is involved in substrate binding. The experimental data are compatible with this hypothesis.