Effects of some S-blocked glutathione derivatives on the prevalent glyoxalase II (a form) of rat liver.

The prevalent glyoxalase II (S-2-hydroxyacylglutathione hydrolase, EC 3.1.2.6, a form) of rat liver cytosol has been studied with a series of seven S-blocked glutathione derivatives. At pH 7.4 and 20 degrees C, only p-nitrobenzyl-S-glutathione was found completely inactive. All the other derivatives are linear competitive inhibitors of the enzyme. Ki values using S-D-lactoylglutathione as substrate are reported. Alkyl-S-glutathiones are weak inhibitors and their inhibition increases with the decrease of the length of the alkyl chain. The best inhibitors are those glutathione derivatives which contain a thioester bond (carbobenzoxy- and p-nitrocarbobenzoxy-S-glutathione) or a carbonyl group (p-chlorophenacyl-S-glutathione). Inhibition by carbobenzoxy-S-glutathione seems to be more complex since the double reciprocal plot shows deviation from linearity at low substrate concentration.