NITRATION OF GAMMA-TOCOPHEROL AND OXIDATION OF ALPHA-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 prese nce of H2O2, leading to self-inactivation and formation of a potent en zyme-bound oxidant, We report in this study that lipid peroxidation of L-cu lecithin liposomes was enhanced greatly during the SOD/H2O2 reac tion 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/H2 O2 in saturated 1,2-dilauroyl-sn-glycero-3-phosphatidylc liposomes, Th e 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/N O2-, the major product identified was 5-NO2-gamma-TH. Nitrone spin tra ps significantly inhibited the formation of alpha-tocopheryl quinone a nd 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 p robe for investigating the peroxidase activity of familial Amyotrophic Lateral Sclerosis-linked SOD mutants.