Purification and characterization of glutamic acid dehydrogenase and α-ketoglutaric acid reductase from Peptococcus aerogenes

Two NAD-dependent enzymes involved in glutamic acid metabolism have been isolated from cell-free extracts of P. aerogenes. One enzyme, glutamic acid dehydrogenase, was shown to oxidatively deaminate glutamic acid yielding α-ketoglutaric acid in the presence of NAD but not NADP. The other enzyme, an NADH-requiring α-ketoglutarate reductase, reduced the α-keto acid to α-hydroxy-glutarate. The two NAD-dependent enzymes were separated, purified, and characterized. The results indicate that glutamic acid dehydrogenase, an enzyme not frequently implicated in anaerobic glutamate metabolism, is a predominating protein in extracts of P. aerogenes grown in the presence of glutamate. Kinetic data showed that the equilibrium of the latter reaction favored the direction of keto acid reduction.