The Mechanism of the Formation of γ-Glutamylpeptides during L-Glutamic Acid Fermentation Contributed Solely by γ-Glutamyltranspeptidase

Abstract

The enzyme of Corynebacterium glutainicum that catalyzes the formation of various γ-L(D)-glutamylpeptides by the reversal of hydrolysis was found to be γ-glutamyltranspepti-dase. The enzyme catalyzed γ-L(D)-glutamyl transfer reaction from various γ-L(D)-glutamyl-peptides including glutathione. The susceptibility of D-isomers was 17% of that of L-isomers. Many kinds of α-L-amino acids and peptides such as γ-L-Glu-L-Glu could be γ-glutamyl ac-ceptors. These findings offered full explanation on the formation of γ-L-glutamylpeptides in the L-glutamic acid fermentation. In the supposed mechanism, γ-L-GIu-L-Glu is formed mainly by the reversal of hydrolysis from L-glutamic acid being richly produced by the bacteria. The other four minor peptides are formed by the γ-glutamyltranspeptidation from γ-L-Glu-L-Glu to some α-L-amino acids and to γ-L-GIu-L-Glu itself in the broths. The enzyme was found to be widely distributed among bacteria, especially in some strains of Corynebacteriun, Bacillus, Erwinea, Serratia, Pseudomonas, Achromobacter, and Alcaligenes.