Glutathione reductase inactivation by Cu(II)H2O2:: influence of thiols and catecholamines

Yeast glutathione reductase (GR) was inactivated by the Cu-Fenton system (FS; Cu(II)/H2O2). Several monothiols, namely cysteine, N-acetylcysteine, mercaptopropionylglycine) and penicillamine increased GR inactivation 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 about 0.2 mM, but higher concentrations were less effective, specially during short-time incubations. Oxidized GSH (GSSG) and the disulfide trypanothione protected GR against CU(II)H2O2. Generally speaking, the effect of thiols on GR inactivation correlated with the latter compounds capability for generating hydroxyl radicals, in the presence of CU(II)H2O2. Cu(ll)-complexing agents(EDTA and DETAPAC) at adequate concentrations prevented GR inactivation by CU(II)H2O2. The Cu(II)/RSH systems (H2O2 omitted) also inactivated GR but to a lesser degree than the corresponding CU(II)/H2O2/RSH systems. Superoxide dismutase and catalase prevented GR inactivation by the CU(II)/RSH systems thus proving the role of superoxide radical and H2O2 respectively. Catecholamines (epinephrine-nor-epinephrine, Dopamine, 60H-Dopamine, L-DOPA, DOPAC), pyrogallol and the dicatechol nor-dihydroguaiaretic acid) enhanced, like thiols, 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, superoxide anions and H2O2. A similar reaction mechanism would operate with the Cu(ll)/H2O2/catecholamine and related systems.