Ornithine transaminase in Neurospora and its relation to the biosynthesis of proline

Abstract

An enzyme present in extracts of N. crassa mycelium transfers the delta-amino group of L-ornithine to alpha-ketoglutaric acid with the formation of glutamic acid and glutamic gamma-semi-aldehyde. The latter compound is partly converted, probably spontaneously, to [DELTA]1-pyrroline-5-carboxylic acid and there is some evidence that this is in enzyme-catalysed equilibrium with another closely related compound. If o-aminobenzaldehyde is added to trap the pyrrolinecarboxylic acid, the reaction goes to completion; otherwise, it comes to equilibrium with about 80% of the ornithine deaminated, after starting with equimolar amts. of ornithine and alpha-ketoglutarate. Evidence was obtained for the synthesis of ornithine from glutamic gamma-semialdehyde and glutamate by the same enzyme prepns. Both mycelial extracts and intact mycelium of mutant strains of Neurospora having a growth requirement for ornithine showed a normal amount of ornithine transaminase activity.