title: Mitochondrial respiration scavenges extramitochondrial superoxide anion via a nonenzymatic mechanism.
abstract: We determined that mitochondrial respiration reduced cytosolic oxidant stress in vivo and scavenged extramitochondrial superoxide anion (O2-.) in vitro. First, Saccharomyces cerevisiae deficient in both the cytosolic antioxidant cupro-zinc superoxide dismutase (Cu,Zn-SOD) and electron transport (Rho0 state) grew poorly (P < 0.05) in 21% O2 compared with parent yeast and yeast deficient only in electron transport or Cu,Zn-SOD, whereas anaerobic growth was the same (P > 0.05) in all yeast. Second, isolated yeast and mammalian mitochondria scavenged extramitochondrial O2-. generated by xanthine/xanthine oxidase. Yeast mitochondria scavenged 42% more (P < 0.05) extramitochondrial O2-. during pyruvate/malate-induced respiration than in the resting state. Addition of either antimycin (respiratory chain inhibitor) or FCCP (respiratory chain uncoupler) prevented increased O2-. scavenging. Mitochondria isolated from yeast deficient in the mitochondrial manganous superoxide dismutase (Mn-SOD) increased (P < 0.05) O2-. scavenging 56% during respiration. This apparent SOD activity, expressed in units of SOD activity per milligram of mitochondrial protein, was the same (9 +/- 0.6 vs. 10 +/- 1.0; P = 0.43) as the O2-. scavenging of mitochondria with Mn-SOD, suggesting that respiration-dependent mitochondrial O2-. scavenging was nonenzymatic. Finally, isolated rat liver and lung mitochondria also increased (P < 0.05) O2-. scavenging during respiration. We speculate that respiring mitochondria, via the protonmotive pump, present a polarized, proton-rich surface that enhances nonenzymatic dismutation of extramitochondrial O2-. and that this is a previously unrecognized function of mitochondrial respiration with potential physiological ramifications.
authors.affiliation: Webb-Waring Institute for Biomedical Research, Denver, Colorado, USA.
authors.forename: D M
authors.initials: DM
authors.lastname: Guidot
authors.forename: J E
authors.initials: JE
authors.lastname: Repine
authors.forename: A D
authors.initials: AD
authors.lastname: Kitlowski
authors.forename: S C
authors.initials: SC
authors.lastname: Flores
authors.forename: S K
authors.initials: SK
authors.lastname: Nelson
authors.forename: R M
authors.initials: RM
authors.lastname: Wright
authors.forename: J M
authors.initials: JM
authors.lastname: McCord
mesh_terms: D000818:Animals; D000838:Anions / Q000378:metabolism; D000968:Antimycin A / Q000031:analogs & derivatives / Q000494:pharmacology; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism*; D004579:Electron Transport / Q000187:drug effects; D005656:Fungal Proteins / Q000378:metabolism; D008168:Lung / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D008928:Mitochondria / Q000378:metabolism*; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism; D018384:Oxidative Stress; D010101:Oxygen Consumption; D011522:Protons; D051381:Rats; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism*; D014969:Xanthine Oxidase / Q000378:metabolism
chemical_list: D000838:Anions; D005656:Fungal Proteins; D011522:Protons; D013481:Superoxides; C032456:antimycin; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D000968:Antimycin A; D014969:Xanthine Oxidase