Oxidation of Methionine by Human Polymorphonuclear Leukocytes

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Abstract

Studies of the photosensitized oxidation have demonstrated that photodynamic oxidation of methionine is mediated by singlet oxygen (1O2). In this study, we demonstrated that phagocytosing human polymorphonuclear leukocytes (PMN), but not resting PMN, oxidized both intracellular and extracellular methionine to methionine sulfoxide. N-ethylmaleimide, which inhibits phagocytosis and cellular metabolism, inhibited the oxidation of methionine. Neutrophils from patients with chronic granulomatous disease did not oxidize methionine even in the presence of phagocytosis. The oxidation of methionine by phagocytosing normal PMN was inhibited by 1O2 quenchers, (1.4-diazabicyclo-[2,2,2]-octane, tryptophan, NaN3), myeloperoxidase (MPO) inhibitors (NaN3, KCN) and catalase. In contrast, superoxide dismutase, ethanol, and mannitol had no effect. Furthermore, 1O2 quenchers did not interfere with the production of superoxide (O2−) by phagocytosing PMN. The combination of catalase and SOD did not enhance the inhibition of methionine by phagocytosing PMN. On the other hand, deuterium oxide stimulated the oxidation of methionine by PMN almost 200%.

Authors

Min-Fu Tsan, Jasmine W. Chen