title: Superoxide reactivates nitric oxide-inhibited catalase.
abstract: Catalase binds nitric oxide (NO) to generate ferricatalase-NO, an inhibited form of the enzyme. Superoxide (O2-) is also an inactivator of the enzyme. We found, however, that O2- efficiently converted the inhibited ferricatalase-NO to the active ferricatalase without producing detectable intermediates. The reaction slowed down when O2- was disproportionated to H2O2 and O2 by superoxide dismutase, but H2O2 could displace the heme-bound NO slowly to regenerate ferricatalase. Reactivation was observed even under simultaneous generation of NO and O2-, suggesting that ferricatalase-NO reacts with O2- fast enough to compete with the rapid reaction of O2- and NO. Formation of peroxynitrite by the simultaneous generation of NO and O2- was only partially inhibited by ferricatalase, presumably due to slow binding of NO to catalase in comparison with the reaction of NO and O2-.
authors.affiliation: Department of Biochemistry, Kangwon National University, Chunchon, South Korea.
authors.forename: Y S
authors.initials: YS
authors.lastname: Kim
authors.forename: S
authors.initials: S
authors.lastname: Han
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002374:Catalase / Q000037:antagonists & inhibitors* / Q000187:drug effects; D002417:Cattle; D004793:Enzyme Reactivators / Q000494:pharmacology*; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D009566:Nitrates / Q000378:metabolism; D009569:Nitric Oxide / Q000494:pharmacology*; D016877:Oxidants / Q000378:metabolism; D013482:Superoxide Dismutase / Q000378:metabolism; D013481:Superoxides / Q000494:pharmacology*
chemical_list: D004793:Enzyme Reactivators; D009566:Nitrates; D016877:Oxidants; D013481:Superoxides; C039642:peroxynitric acid; D009569:Nitric Oxide; D006861:Hydrogen Peroxide; D002374:Catalase; D013482:Superoxide Dismutase