MODIFICATION OF ARGININE RESIDUES AT THE SUBSTRATE-BINDING SITE OF YEAST GLUTATHIONE-REDUCTASE

Yeast glutathione reductase (CR) was inactivated by phenylglyoxal (PG) , which specifically modifies arginine residues of the enzyme. Inactiv ation followed psuedo-first order rate kinetics. There was no reversib le complex formation prior to inactivation. Analysis of the kinetic da ta showed the order of reaction to be unity with respect to the modifi er. Inactivation of GR was completely prevented by the presence of oxi dised glutathione (GSSG), whereas NADP gave only partial protection. S toichiometric studies showed that around four arginine residues per su bunit were modified by PG in the absence of GSSG, whereas only one was modified in its presence. From these observations, it is concluded th at essential arginine residues are present at the substrate binding si te.