Modification of erythrocyte enzyme activities by persulfides and methanethiol: possible regulatory role.

Sulfhydryl modification of 22 human erythrocyte enzymes was achieved by exposing intact erythrocytes, hemolysates, and partially purified enzymes to persulfides (RSSH) generated nonenzymatically from cystine in the presence of pyridoxal phosphate and mercaptopyruvate, which donates its sulfur to suitable acceptors with the mediation of the carrier enzyme, mercaptopyruvate sulfurtransferase (EC 2.8.1.2). The inhibition pattern was qualitatively similar for persulfides and that previously reported by us for the methylthio-group donor, methyl methanethiosulfonate. Thirteen activities were inhibited, and 9 were minimally or not at all affected. Pyruvate kinase was similarly modified by all systems in terms of phosphoenolpyruvate kinetics, thermostability, and interaction with the negative effector ATP. Partial-to-complete reversal of inhibition was documented in a subset of activities inhibited by mercaptopyruvate upon 30-min incubation with 1 mM dithiothreitol. A possible physiologic role for methylthio groups and for persulfides is discussed.