Kinetics of coupled reactions catalyzed by aspartate aminotransferase and glutamate dehydrogenase

Liver mitochondrial aspartate aminotransferase and glutamate dehydrogenase catalyze following sequence of reactions: see formula in text. 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 slopes of the linear part of this curve is a linear function of transaminase concentration. At high concentration (approximately or equal to 10 microM) of both enzymes the lag phase, as observed after rapid mixing of the two 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.