[Regulation and physiological significance of aspartate-ammonium lyase (aspartase) of Pseudomonas fluorescens type R (author's transl)].

The biosynthesis of aspartate-ammonium lyase, the enzyme which is induced by aspartic acid, is specifically repressed by fumaric acid. In the presence of aspartate, the enzyme permits the deamination of this compound by the cell. Aspartic acid is converted into fumaric acid which is an intermediate in the Krebs'cycle. The reaction may be considered as an anaplerotic sequence. In the absence of aspartic acid in the culture medium, its role is anabolic; the enzyme catalyses the biosynthesis of this amino acid. Therefore it appears that the reversible reaction fumarate + NH3 = aspartate catalysed by aspartase is included in amphibolic processes.