Broadly, the objectives of the present studies are to obtain quantitative information on reaction-transients in enzyme-catalyzed reactons which is suitable to permit resolution of presently equivalent models for catalysis. Temperature-jump relaxation and stopped-flow instrumentation are the principal kinetic tools employed. Reactions under current investigation include those catalyzed by enolase (EC 4.2.1.11) and creatine kinase (EC 2.7.3.2) - the focal point of this work is evaluation of the significance of observed two-step substrate binding mechanisms to specificity (Km) and reactivity (Vmax) in the systems. Preliminary evidence suggests that catalytic activity can be correlated with partitioning of ES complexes between the two isomeric states in such fashion that one state can be identified as uniquely reactive. Comparison of structural differences between the reactive and unreactive ES complexes should then provide the basis for factors responsible for catalytic action. Complementary rapid-kinetic and spectrophotometic studies designed to identify interacting components in multi-redox biological particles (e.g., xanthine oxidase) have also been initiated.