Generation of hydrogen peroxide by incidental metal ion-catalyzed autooxidation of glutathione.

Autooxidation of reduced glutathione in 50 mM buffer at pH 7.9 is indetectably slow in the presence of 1 mM DETAPAC, EDTA, TET, or tripyridine, but passing buffer through Chelex resin was insufficient to remove traces of catalytically active metals. Production of hydrogen peroxide during glutathione autooxidation was catalyzed by traces of Fe+2 or Cu+2, and to a much lesser extent by Cu+1 and Ni+2, but not to a detectable extent by Na+1, K+1, Fe+3, Al+3, Cd+2, Zn+2, Ca+2, Mg+2, Mn+2, or Hg+2. Cysteine was a much better precursor for hydrogen peroxide production than were cysteine sulfinic or sulfonic acids. The chelators EGTA, NTA, bipyridine, dimethyl glyoxime, salicylate, and Desferal were ineffective at preventing autooxidation. EDDA and 8-hydroxyquinoline were partially effective. Catalase could completely prevent the accumulation of detectable H2O2, but superoxide dismutase was only slightly inhibitory. Hydroxyl radical and singlet oxygen quenching agents (mannitol and histidine) stimulated. A mechanism for the production of H2O2 during trace metal catalyzed oxidation of glutathione is proposed, involving glutathione-complexed metal and dissolved oxygen. Although a radical intermediate can not be ruled out, no radical initiated chain reaction is necessary.