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Alpha-ketoglutarate as an intermediate in glutamate metabolism by Peptococcus aerogenes

1972; Canadian Science Publishing; Volume: 18; Issue: 6 Linguagem: Inglês

10.1139/m72-135

1480-3275

William M. Johnson, D. W. S. Westlake,

Amino Acid Enzymes and Metabolism

The pathway from glutamic acid to α-hydroxyglutaric acid in Peptococcus aerogenes proceeds via α-ketoglutaric acid and is mediated by two NAD-dependent enzymes. One enzyme, an NAD-dependent glutamic acid dehydrogenase, oxidatively deaminates glutamic acid to α-ketoglutaric acid. The other enzyme, α-ketoglutaric acid reductase, reduces α-ketoglutaric acid to α-hydroxyglutaric acid in the presence of NADH. The demonstration of a very low level of α-ketoglutaric acid dehydrogenase activity in crude cell-free extracts indicates that the primary metabolic pathway for glutamic acid carbons proceeds via α-hydroxyglutaric acid and not via the TCA cycle. Potential energy-yielding mechanisms are discussed relative to the known specific distribution of glutamic acid carbon atoms in fermentation products.