An l-glutamic acid decarboxylase from barley

Abstract

Aqueous extracts from barley roots contained an active L-glutamic acid decarboxylase, but did not de-carboxylate L-aspartic acid, L-arginine, L-histidine, L-tryptophan or L-tyrosine at measurable rates. Active precipitates were obtained from aqueous extracts by treatment with ammonium sulfate, the enzyme being stable under these conditions. Almost quantitative decarboxylation was achieved using redissolved precipitates and the product was identified by chromatography as gamma -aminobutyric acid. A calculation of the Michaelis constant gave a value of 9.6 x 0.001 [image], allowance being made by inhibition by high substrate concns. The pH relationships and reactions to inhibitors of the barley enzyme were similar to those previously described. It was suggested that the natural occurrence of gamma-aminobutyric acid may be ascribed to the functioning of the enzyme in vivo.