title: Source of superoxide anion radical in aerobic mixtures consisting of NAD[P]H, 5-methylphenazinium methyl sulfate and nitroblue tetrazolium chloride.
abstract: The source of superoxide anion radical (O2-.) in aerobic mixtures consisting of NAD[P]H, 5-methylphenazinium methyl sulfate (or its 1-methoxy derivative) and tetrazolium salt was investigated using superoxide dismutase (SOD), Mn(II), ferricytochrome-C, and epinephrine as probes. NAD[P]H + phenazine + O2 was found to reduce nitroblue tetrazolium, iodonitrotetrazolium, and thiazolyl blue in a manner sensitive to agents that dismutase O2-., viz., SOD and Mn(II). It also mediated the reduction of ferricytochrome-C, and augmented the autooxidation of epinephrine to the adrenochrome, without a tetrazolium salt present in the medium. The autooxidation of epinephrine, but not the reduction of ferricytochrome-C, was found to be sensitive to SOD. Nitroblue tetrazolium, either singly or in combination with SOD, did not stimulate the reduction of ferricytochrome-C. The oxidation of NADH, mediated by a catalytically low concentration of phenazine(+O2), was augmented two-fold by SOD. These observations are consistent with, and lend support to, a scheme of redox events (Scheme-3) wherein it is proposed that the source of O2-. in the NAD[P]H + phenazine + tetrazolium(+O2) system is the reduced phenazine, that the tetrazoinyl radical (a one-electron reduction product of tetrazolium) may not reduce O2 to O2-., that the redox reaction between semiquinone radicals of phenazine and O2 is reversible, and that the disproportionation of semiquinone radicals constitutes an important rate-limiting reaction in the expression of phenazine redox couple.
authors.affiliation: Department of Medicine, Nizam's Institute of Medical Sciences, Hyderabad, India.
authors.forename: U M
authors.initials: UM
authors.lastname: Rao
mesh_terms: D000332:Aerobiosis; D003574:Cytochrome c Group; D004837:Epinephrine; D005609:Free Radicals; D066298:In Vitro Techniques; D008773:Methylphenazonium Methosulfate; D009243:NAD; D009249:NADP; D009580:Nitroblue Tetrazolium; D010084:Oxidation-Reduction; D013481:Superoxides
chemical_list: D003574:Cytochrome c Group; D005609:Free Radicals; D009243:NAD; D013481:Superoxides; D009580:Nitroblue Tetrazolium; D008773:Methylphenazonium Methosulfate; D009249:NADP; D004837:Epinephrine