Formation of reducing radicals on radiolysis of glutathione and some related compounds in aqueous solution

Abstract

The ˙OH-induced oxidation of glutathione in basic aqueous solution has been found to produce the sulphur-centred radical GS˙(GSSG–˙) and two reducing radicals. Decarboxylation, considered to be initiated by ˙OH radical addition to the nitrogen of the amino group on the γ-glutamyl unit, was found to be effective for methylated glutathione (GSMe) and opthalmic acid (GMe) but of minor importance for glutathione. The G-values for the strongly reducing α-amino radicals formed on decarboxylation were found to be 3.3, 3.3, and 0.5 for GSMe, GMe, and GSH, respectively, at pH 10.5. The formation of an additional strongly reducing radical with G= 2.2 at pH 10.5 was demonstrated by measuring the electron-transfer to p-nitroacetophenone (PNAP). This radical is not formed from GSMe or GMe. We suggest that the underlying mechanism for the formation of this species is based on pH-dependent conformational changes of glutathione followed by ˙OH addition to the cysteine sulphur, or hydrogen abstraction from the CH2 group in the α-position to the sulphur leading to the formation of a reducing carbon-centred radical.