Reinvestigation of the roles of the carboxyl groups of glutathione with yeast glyoxalase I. Implications as to the mechanism and coenzymic role of glutathione.

A number of carboxyl-substituted S-blocked glutathiones have been shown to be competitive inhibitors of yeast glyoxalase I at 25 degrees C, pH 6.6. Amidation of the glycyl carboxyl group of S-(p-bromobenzyl)glutathione has no appreciable effect on binding whilst methylation reduces binding by 8.9-fold, indicating a steric constraint and the possible presence of a hydrogen bond in this region of the enzyme. Amidation of both carboxyl groups of S-(p-bromobenzyl)glutathione reduces binding significantly by 237-fold; this result agrees with electrostatic interaction of the Glu COO- group with a group located within the enzyme surface as opposed to the Gly COO- group, previously proposed.