The oxidation of sulphydryl compounds by hydrogen peroxide

Abstract

The course of oxidation was followed polarimetrically. The rate of oxidation, at pH 2.1, in the presence of Cu was proportional to the H2O2 concentration and independent of the amount of cysteine. In the presence of Fe, the rate was proportional to the concentrations of Fe and cysteine and was inhibited by an increase in H2O2. Phosphate did not affect Cu catalysis at pH 2.1 or pH 4.6, but Fe catalysis was inhibited at both reactions. Copper catalysis was unaffected by pyrophosphate, but Fe catalysis was inhibited quantitatively. HCN activated Fe at pH 2.1 and did not seem to affect Cu. Both Cu and Fe were inhibited at pH 4.6. Ferricyanide inhibited both Cu and Fe catalysis. Haemocyanin had no catalytic effect, but at pH 2.1 it decomposed giving catalytically active Cu. In the presence of Cu the oxidation of glutathione was similar to that of cysteine, but the effects were quite different when Fe was the catalyst.