Nitration of γ-tocopherol and oxidation of α-tocopherol by copper-zinc superoxide dismutase H2O2/NO2-:: Role of nitrogen dioxide free radical

Copper-zinc superoxide dismutase (Cu,Zn-SOD) is the antioxidant enzyme that catalyzes the dismutation of superoxide (O2(.-)) to O-2 and H2O2. In addition, Cu,ZnSOD also exhibits peroxidase activity in the presence of H2O2, leading to self-inactivation and formation of a potent enzyme-bound oxidant, We report in this study that lipid peroxidation of L-cu lecithin liposomes was enhanced greatly during the SOD/H2O2 reaction in the presence of nitrite anion (NO2-) with or without the metal ion chelator, diethylenetriaminepentacetic acid. The presence of NO2- also greatly enhanced alpha-tocopherol (alpha-TH) oxidation by SOD/H2O2 in saturated 1,2-dilauroyl-sn-glycero-3-phosphatidylc liposomes, The major product identified by HPLC and UV-studies was alpha-tocopheryl quinone, When 1,2-diauroyl-sn-glycero-3-phosphatidylcholine liposomes containing gamma-tocopherol (gamma-TH) were incubated with SOD/H2O2/NO2-, the major product identified was 5-NO2-gamma-TH. Nitrone spin traps significantly inhibited the formation of alpha-tocopheryl quinone and 5-NO2-gamma-TH. NO2- inhibited H2O2-dependent inactivation of SOD, A proposed mechanism of this protection involves the oxidation of NO2- by an SOD-bound oxidant to the nitrogen dioxide radical ((NO2)-N-.). In this study, we have shown a new mechanism of nitration catalyzed by the peroxidase activity of SOD, We conclude that NO2- is a suitable probe for investigating the peroxidase activity of familial Amyotrophic Lateral Sclerosis-linked SOD mutants.