Kinetics of Coupled Reactions Catalyzed by Aspartate Aminotransferase and Glutamate Dehydrogenase

Abstract

Liver mitochondrial aspartate aminotransferase and glutamate dehydrogenase catalyze the following sequence of reactions: .**GRAPHIC**. In the presence of a slight excess of dehydrogenase, the time course of NADPH oxidation resulting from the overall reaction goes through a lag phase and reaches a linear phase. The slope of the linear part of this curve is a linear function of transaminase concentration. At high concentration (.apprxeq. 10 .mu.M) of both enzymes the lag phase, as observed after rapid mixing of the 2 enzymes in a Durrum stopped-flow spectrophotometer, is shorter than that predicted from the kinetic parameters determined for the separate reactions catalyzed by each enzyme.