DOES THE AEROBIC XANTHINE OXIDASE REACTION GENERATE SINGLET OXYGEN?*

Abstract— The aerobic xanthine oxidase reaction causes the co-oxidation of 2,5-dimethylfuran to cis-diacetylethylene and the bleaching of rubrene tetracarboxylate. These actions were suppressed by superoxide dismutase, catalase, desferoxamine and by benzoate and other hydroxyl radical scavengers. The bleaching of rubrene tetracarboxylate was not enhanced in D₂0. These results suggest that OHv, generated from O₂^- plus H₂O₂ by an iron-catalyzed Haber Weiss reaction, was the responsible agent and that singlet oxygen was not detectably involved. Control experiments, in which singlet oxygen was generated photochemically, demonstrated that replacement of H₂O by D₂O caused the expected enhancement of the chemical reactivity of singlet oxygen under the conditions of these experiments and that O₂^-, at concentrations achieved by the xanthine oxidase reaction, did not detectably quench singlet oxygen. We conclude that singlet oxygen, if produced at all during the aerobic xanthine oxidase reaction, cannot exceed 0.1% of the production of O₂^-.