The mechanism of the glyoxalase I reaction, and the effect of ophthalmic acid as an inhibitor

Abstract

Ophthalmic acid, an analogue of glutathione that occurs in calf lens was a competitive inhibitor in the reaction catalyzed by glyoxalase. I. The velocity of the enzyme reaction was s symmetrical function of the concentrations of methylglyoxal and glutathione (GSH). This result suggested that the hemimercaptal, CH3 . CO . CH (OH) . SG. which was formed on mixing the components, was the substrate for glyoxalase I. Some supporting evidence for this suggestion was provided, and a different mechanism, previously proposed was excluded. The initial rate of formation of the hemimercaptal was proportional to the concentration of methylglyoxal but independent of the concentration of glutathione. The rate-determining step in the formation of the hemimercaptal was probably the liberation of free methylglyoxal from a hydrate. At low concentrations of methylglyoxal and high concentrations of enzyme the rate of the enzymic formation of S-lactoylglutathione was affected by the rate of the (non-enzymic) formation of hemimercaptal. The retardation caused by a relatively high concentration of glutathione was ascribed to the action of free glutathione as an inhibitor (the hemimercaptal being the substrate).