title: Biologically relevant mechanism for catalytic superoxide removal by simple manganese compounds.
abstract: Nonenzymatic manganese was first shown to provide protection against superoxide toxicity in vivo in 1981, but the chemical mechanism responsible for this protection subsequently became controversial due to conflicting reports concerning the ability of Mn to catalyze superoxide disproportionation in vitro. In a recent communication, we reported that low concentrations of a simple Mn phosphate salt under physiologically relevant conditions will indeed catalyze superoxide disproportionation in vitro. We report now that two of the four Mn complexes that are expected to be most abundant in vivo, Mn phosphate and Mn carbonate, can catalyze superoxide disproportionation at physiologically relevant concentrations and pH, whereas Mn pyrophosphate and citrate complexes cannot. Additionally, the chemical mechanisms of these reactions have been studied in detail, and the rates of reactions of the catalytic removal of superoxide by Mn phosphate and carbonate have been modeled. Physiologically relevant concentrations of these compounds were found to be sufficient to mimic an effective concentration of enzymatic superoxide dismutase found in vivo. This mechanism provides a likely explanation as to how Mn combats superoxide stress in cellular systems.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA.
authors.forename: Kevin
authors.initials: K
authors.lastname: Barnese
authors.forename: Edith Butler
authors.initials: EB
authors.lastname: Gralla
authors.forename: Joan Selverstone
authors.initials: JS
authors.lastname: Valentine
authors.forename: Diane E
authors.initials: DE
authors.lastname: Cabelli
mesh_terms: D000975:Antioxidants / Q000378:metabolism / Q000494:pharmacology; D002254:Carbonates / Q000378:metabolism / Q000494:pharmacology; D002384:Catalysis; D066298:In Vitro Techniques; D007700:Kinetics; D008024:Ligands; D008345:Manganese / Q000378:metabolism / Q000494:pharmacology*; D008954:Models, Biological; D009942:Organometallic Compounds / Q000378:metabolism / Q000494:pharmacology; D018384:Oxidative Stress / Q000187:drug effects; D013482:Superoxide Dismutase / Q000378:metabolism; D013481:Superoxides / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D000975:Antioxidants; D002254:Carbonates; D008024:Ligands; D009942:Organometallic Compounds; D013481:Superoxides; D008345:Manganese; C045327:manganese carbonate; D013482:Superoxide Dismutase; C406182:manganese phosphate