Effects of Sulfhydryl Compounds on Lipid Oxidations Catalyzed by Copper and Heme

Effects of cysteine and glutathione on copper- and heme-catalyzed oxidation of methyl linoleate were studied in a model emulsion system. In the copper-catalyzed system, cysteine exerted a strong prooxidative effect, and this prooxi’dative effect increased as the concentration of cysteine increased. Furthermore, oxidized glutathione did not have a prooxidative effect, whereas reduced glutathione showed prooxidative activity. Blocking the sulfhydryl group by treatment of cysteine with iodoacetic acid completely eliminated the prooxidative activity of cysteine. In the heme-catalyzed system, cysteine showed an antioxidative effect that increased as concentration of cysteine increased. This antioxidative effect of cysteine was practically eliminated by treatment with iodoacetic acid. Reduced glutathione showed a greater antioxidative effect than oxidized glutathione. In the presence of sulfhydryl compounds, copper promoted superoxide anion generation whereas heme did not. The addition of cysteine (10 to 1000M) to milk did not inhibit either copper or heme induced lipid oxidation.