Biosynthesis of Glutamic Acid in Saccharomyces : Accumulation of Tricarboxylic Acid Cycle Intermediates in a Glutamate Auxotroph

Aconitaseless glutamic acid auxotroph MO-1-9B ofSaccharomyces grew in glutamic acid-supplemented minimal medium, but failed to grow when glutamic acid was substituted by proline, arginine, ornithine, or glutamine. This mutant was also unable to utilize lactate or glycerol as a carbon source. Under a glutamic acid-limiting condition, by using acetate-1 -14 C as tracer, the mutant accumulated rather large amounts of14 C-citric acid and14 C-succinic acid when compared with the wild-type strain. Under excess glutamic acid supplementation, accumulation of citric acid and succinic acid was considerably reduced. When14 C-glutamic acid-(U) was used as tracer,14 C-α-ketoglutaric acid,14 C-citric acid, and14 C-succinic acid were accumulated in the mutant. The citric acid peak was the largest, followed by α-ketoglutaric acid and succinic acid. In the wild-type strain under similar conditions, only small amounts of14 C-citric acid and14 C-succinic acid and no14 C-α-ketoglutaric acid were accumulated.