The Production of Hydroxyl Radicals in Biological Systems

Although aqueous superoxide is a potential fairly strong oxidant 

The production of ethylene from methional (3-thiomethylpropanal) was induced by the oxidation of xanthine by dioxygen catalysed by xanthine oxidase The second-order rate constant for the reaction of hydroxyl radicals with methional was estimated by pulse radiolysis to amount to 8.2 x lO s while the superoxide anion reacted more slowly The short lag period of the ethylene production induced by the oxidation of xanthine could be overcome by the addition of small amounts of hydrogen peroxide. The reaction was inhibited by SOD or by catalase, and by scavengers of hydroxyl radicals, so that the Haber-Weiss reaction was implicated 

A direct Haber-Weiss reaction is generally considered to be far too slow a second-order rate constant of 2.3 s has been estimated from the decomposition of aqueous H Oj by y rays The reaction could be metal catalysed by 

The Fe-EDTA complex catalysed the oxidation of tryptophan and the hydroxyla-tion of salicylate in the presence of a superoxide-generating system, A partial inhibition by diethylenetriaminepenta-acetate was observed for the latter reaction and in the ethylene production from 2-keto-4-thiomethylbutyrate 

The production of hydroxyl radicals was demonstrated by spin-trapping in the autoxidation at pH 11.5 of 6-hydroxydopamine. The reaction was partially inhibited by SOD, by catalase, and by diethylenetriaminepenta-acetate and deferoxamine 

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