Organic free radicals and proteins in biochemical injury: electron- or hydrogen-transfer reactions?

Abstract

The reactions of organic free radicals, acting as either reductants or oxidants, have been studied by pulse radiolysis in neutral aqueous solution at room temperature. Many hydroxyl-substituted aliphatic carbon-centred radicals and one-electron adducts have been shown to be good one-electron reductants, while several oxygen-, sulphurand nitrogen- (but not carbon-) centred free radicals have been shown to be good one-electron oxidants. Several carbon-centred radicals can be reduced rapidly by hydrogen transfer, from undissociated thiol compounds which can thus act as catalysts facilitating the overall reduction of a carbon-centred radical by an electron-donating molecule. Kinetic considerations influenced by the one-electron redox potentials of the radical-molecule couples involved, determine whether a particular reaction predominates. In this paper examples of such reactions, involving a water-soluble derivative of vitamin E (Trolox C) and the coenzyme NADH, are described, together with studies showing ( a ) that even in complex multi-solute systems some organic peroxy radicals can inactiviate alcohol dehydrogenase under conditions where the superoxide radical does not, and ( b ) the superoxide radical can be damaging if urate is also present, and this damage can be reduced by the presence of superoxide dismutase.