STUDIES OF GLUCONEOGENIC MITOCHONDRIAL ENZYMES .2. CONVERSION OF GLUTAMATE TO ALPHA-KETOGLUTARATE BY BOVINE LIVER MITOCHONDRIAL GLUTAMATE DEHYDROGENASE AND GLUTAMATE-OXALOACETATE TRANSAMINASE

Kinetic experiments have been performed on the bovine liver mitochondrial glutamate dehydrogenase and glutamate-oxaloacetate transaminase. The two enzymes have been prepared in pure form from the same mitochondrial extracts. The levels of activity of these two enzymes in mitochondrial extracts have been estimated. The rate of glutamate utilization by these two enzymes has been compared. The results have been normalized according to the levels of enzyme found in crude mitochondrial extracts. The studies of the rate of conversion of glutamate to α-ketoglutarate with pure enzyme are consistent with studies of intact rat liver mitochondria, in that the transaminase pathway is the major route of glutamate oxidation and the main inhibitors of glutamate oxidation by the dehydrogenase are the levels of reduced pyridine nucleotides. Other products of these reactions have considerably less effect as inhibitors. The Michaelis constant of glutamate is considerably higher in the glutamate dehydrogenase than in the transaminase reaction. Therefore the glutamate dehydrogenase reaction would be comparatively more significant in the presence of low concentrations of glutamate. However, on the basis of estimates of enzyme levels, the rate of the transaminase reaction would be greater than the rate of the glutamate dehydrogenase reaction even at rather low concentrations of glutamate. Since none of the products of the transaminase reaction inhibit this reaction until they are present at rather high concentrations, and since the Michaelis constant of glutamate is very much higher than that of oxaloacetate, it is suggested that the concentration of glutamate would be the main regulator of the transaminase reaction. © 1969.