Clxx. the Oxidation of Sulphydryl Compounds by Hydrogen Peroxide. I. Catalysis of Oxidation of Cysteine and Glutathione by Iron

THE oxidation of thiol compounds by oxygen and methylene blue has, in recent years, been very extensively studied, while their oxidation by hydrogen peroxide has suffered almost complete neglect. Abderhalden and Wertheimer [1923] found that cysteine, like other mercaptans, was instantaneously oxidised by hydrogen peroxide in neutral solution, and that this oxidation was unaffected by cyanide. At neutrality an oxidation of the thiol group would be complicated, at any rate in the presence of iron, by the Fenton reaction. Quastel, Stewart and Tunnicliffe [1923] have indeed prepared an oxidation product of this type from glutathione. In acid solution and in the presence of the theoretical amount of hydrogen peroxide the reaction proceeds smoothly with the production of pure oxidised glutathione [Pirie, 1931]. In this paper the results of a study of the oxidation of cysteine and glutathione to the corresponding disulphides will be given while in a later one a more deep-seated oxidation will be described. The former action is catalysed by iron, copper and thiocarbamide while the latter is catalysed by vanadium, titanium and molybdenum. The following elements have, in acid solution, either no action or a very slight one: Ag, As, Be, Co, Cr, Hg, Mn, Ni, Pb, U, W, Zn.