title: Pathways of peroxynitrite oxidation of thiol groups.
abstract: Peroxynitrite mediates the oxidation of the thiol group of both cysteine and glutathione. This process is associated with oxygen consumption. At acidic pH and a cysteine/peroxynitrite molar ratio of < or = 1.2, there was a single fast phase of oxygen consumption, which increased with increasing concentrations of both cysteine and oxygen. At higher molar ratios the profile of oxygen consumption became biphasic, with a fast phase (phase I) that decreased with increasing cysteine concentration, followed by a slow phase (phase II) whose rate of oxygen consumption increased with increasing cysteine concentration. Oxygen consumption in phase I was inhibited by desferrioxamine and 5,5-dimethyl-1-pyrroline N-oxide, but not by mannitol; superoxide dismutase also inhibited oxygen consumption in phase I, while catalase added during phase II decreased the rate of oxygen consumption. For both cysteine and glutathione, oxygen consumption in phase I was maximal at neutral to acidic pH: in contrast, total thiol oxidation was maximal at alkaline pH. EPR spin-trapping studies using N-tert-butyl-alpha-phenylnitrone indicated that the yield of thiyl radical adducts had a pH profile comparable with that found for oxygen consumption. The apparent second-order rate constants for the reactions of peroxynitrite with cysteine and glutathione were 1290 +/- 30 M-1.S-1 and 281 +/- 6 M-1.S-1 respectively at pH 5.75 and 37 degrees C. These results are consistent with two different pathways participating in the reaction of peroxynitrite with low-molecular-mass thiols: (a) the reaction of the peroxynitrite anion with the protonated thiol group, in a second-order process likely to involve a two-electron oxidation, and (b) the reaction of peroxynitrous acid, or a secondary species derived from it, with the thiolate in a one-electron transfer process that yields thiyl radicals capable of initiating an oxygen-dependent radical chain reaction.
authors.affiliation: Departamento de Bioquímica, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay.
authors.forename: C
authors.initials: C
authors.lastname: Quijano
authors.forename: B
authors.initials: B
authors.lastname: Alvarez
authors.forename: R M
authors.initials: RM
authors.lastname: Gatti
authors.forename: O
authors.initials: O
authors.lastname: Augusto
authors.forename: R
authors.initials: R
authors.lastname: Radi
mesh_terms: D002374:Catalase / Q000494:pharmacology; D003545:Cysteine / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D016166:Free Radical Scavengers / Q000494:pharmacology; D005978:Glutathione / Q000378:metabolism; D007700:Kinetics; D009566:Nitrates / Q000378:metabolism*; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000187:drug effects; D013438:Sulfhydryl Compounds / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000494:pharmacology
chemical_list: D016166:Free Radical Scavengers; D009566:Nitrates; D013438:Sulfhydryl Compounds; C039642:peroxynitric acid; D002374:Catalase; D013482:Superoxide Dismutase; D005978:Glutathione; D003545:Cysteine