Biosynthèse de l'arginine chez la levure I. Le sort de la Nα-acétylornithine

Abstract

An enzyme, transferring the acetyl group of N-α-acetylornithine to the amino group of glutamate, has been demonstrated for Saccharomyces cerevisiae. On the other hand, the enzymic reduction of N-α-acetylglutamate with the formation of N-α-acetyl-glutamic-γ-semialdehyde has been reported previously. The absence of transacetylase in an arginine-requiring mutant (gene ar₇) as well as the above findings prove that:

• 1.

  1. The biosynthesis of ornithine, in yeast, proceeds through acetylated intermediates.

• 2.

  2. The transacetylase is the only functional pathway for the conversion of N-α-acetylornithine to ornithine, in spite of the simultaneous presence of an N-α-acetylornithinase (N-α-acetylornithine amidohydrolase).

At least two steps in the biosynthesis of ornithine are repressible by arginine.