SIGNIFICANCE OF THE INTRAMOLECULAR TRANSFORMATION OF GLUTATHIONE THIYL RADICALS TO ALPHA-AMINOALKYL RADICALS - THERMOCHEMICAL AND BIOLOGICAL IMPLICATIONS

Product studies have been undertaken on the OH. radical-induced oxidat ion of glutathione in N2O-saturated aqueous solutions. Ammonia has bee n found to be a prominent product with G values around 2.5-2.9 x 10(-7 ) J mol(-1) from pH 6 to 10.5. The ammonia is considered to be a produ ct of the disproportionation reaction of the alpha-amino carbon-centre d radicals, formed via the intramolecular transformation of glutathion e thiyl radicals, At pH ca. 4-6, the ammonia yield decreases due to th e fact that the transformation reaction slows down with decreasing pH and eventually comes into competition with bimolecular recombination. From the pH dependence of the ammonia yield curve, the equilibrium con stant between the glutathione thiyl radical and the alpha-amino carbon -centred radical is deduced to be >10(4). The strength of the C-H bond alpha to the NH2 and CO2- groups is thus <343 kJ mol(-1). The corresp onding bond energy of the C-H bond alpha to the NH2 and CO2H groups is estimated to be <329 kJ mol(-1). Based on the ammonia formation, cons umption of free SH-groups and the HPLC chromatograms obtained at diffe rent pH values after gamma-irradiation of N2O-saturated glutathione so lutions, the overall reaction mechanism concerning the fate of glutath ione thiyl radicals is proposed. This mechanism and its kinetics indic ate that the intramolecular transformation is one of the principal pat hways of self-removal of glutathione thiyl radicals, which is formed i n various repair processes, in both anaerobic and aerobic conditions.