GLUTATHIONE-REDUCTASE INACTIVATION BY CU( II)H2O2 - INFLUENCE OF THIOLS AND CATECHOLAMINES

Yeast glutathione reductase (GR) was inactivated by the Cu-Fenton syst em (FS; Cu(II)/H2O2). Several monothiols, namely cysteine, N-acetylcys teine, mercaptopropionylglycine) and penicillamine increased GR inacti vation by the CU(II)H2O2, the inactivation reaching maximum values at about 0.20 mM thiol. Glutathione (GSH), dithiothreitol, dihydrolipoic acid and Captopril produced similar effects at concentrations up to ab out 0.2 mM, but higher concentrations were less effective, specially d uring short-time incubations. Oxidized GSH (GSSG) and the disulfide tr ypanothione protected GR against CU(II)H2O2. Generally speaking, the e ffect of thiols on GR inactivation correlated with the latter compound s capability for generating hydroxyl radicals, in the presence of CU(I I)H2O2. Cu(ll)-complexing agents(EDTA and DETAPAC) at adequate concent rations prevented GR inactivation by CU(II)H2O2. The Cu(II)/RSH system s (H2O2 omitted) also inactivated GR but to a lesser degree than the c orresponding CU(II)/H2O2/RSH systems. Superoxide dismutase and catalas e prevented GR inactivation by the CU(II)/RSH systems thus proving the role of superoxide radical and H2O2 respectively. Catecholamines (epi nephrine-nor-epinephrine, Dopamine, 60H-Dopamine, L-DOPA, DOPAC), pyro gallol and the dicatechol nor-dihydroguaiaretic acid) enhanced, like t hiols, GR inactivation by CU(II)H2O2 lesser effects were observed with the Cu(ll)/catecolamines systems (H2O2 omitted). It is concluded that GR inactivation by the Cu(II)/H2O2/RSH systems depends on a chain of reaction producing HO-radicals. That chain involves copper ions, super oxide anions and H2O2. A similar reaction mechanism would operate with the Cu(ll)/H2O2/catecholamine and related systems.