title: Nitration of gamma-tocopherol and oxidation of alpha-tocopherol by copper-zinc superoxide dismutase/H2O2/NO2-: role of nitrogen dioxide free radical.
abstract: Copper-zinc superoxide dismutase (Cu,ZnSOD) is the antioxidant enzyme that catalyzes the dismutation of superoxide (O2*-) to O2 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-alpha-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-phosphatidylcholine 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). 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.
authors.affiliation: Department of Laboratory Medicine and Patholoy, Mayo Clinic, Rochester, MN 55905, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Singh
authors.forename: S P
authors.initials: SP
authors.lastname: Goss
authors.forename: J
authors.initials: J
authors.lastname: Joseph
authors.forename: B
authors.initials: B
authors.lastname: Kalyanaraman
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism; D007536:Isomerism; D007700:Kinetics; D008081:Liposomes; D009573:Nitrites / Q000378:metabolism* / Q000494:pharmacology; D009585:Nitrogen Dioxide / Q000378:metabolism*; D010084:Oxidation-Reduction; D010713:Phosphatidylcholines; D013482:Superoxide Dismutase / Q000378:metabolism*; D014810:Vitamin E / Q000378:metabolism*
chemical_list: D005609:Free Radicals; D007527:Isoenzymes; D008081:Liposomes; D009573:Nitrites; D010713:Phosphatidylcholines; D014810:Vitamin E; D006861:Hydrogen Peroxide; D013482:Superoxide Dismutase; D009585:Nitrogen Dioxide