Metabolism of Bovine Semen. XVII. Oxidative Metabolism of Glutamate

Factors influencing the oxidation of glutamate were studied with washed spermatozoa and with sperm extracts. The mechanism of C02 formation from glut,mate did not involve direct nonoxidative decarboxylation to an appreciable extent, for anoxia inhibited the reaction. Both transaminase and glutamic dehydrogenase appeared to be involved. High levels of transaminase were previously reported and the dehydrogenase was detected spectrophotometrically in extracts from sperm acetone powders. Further evidence of the dehydrogenase was obtained from the stimulating effect of nicotinamide adenine dinucleotide on 14C02 production from glutamate-l-14C by sperm extracts. The reaction involved a-ketoglutarate as a direct intermediate, since it diluted the 1'C0~ from glutamate-12~C. Evidence was obtained that the rate-limiting step occurred before or in the formation of a-ketoglutarate. Identified products of glutamate included aspartate, citrate, malate, succinate, lactate, fumarate, pyrrolidone carboxylate, and a-ketoglutarate.