title: Direct conversion of ferrous myeloperoxidase to compound II by hydrogen peroxide: an anaerobic stopped-flow study.
abstract: Myeloperoxidase (MPO) is one of the essential components of the antimicrobial systems of polymorphonuclear neutrophils. It is unique in having a globin-like standard reduction potential of the ferric/ferrous couple. Here, it is shown that ferrous MPO heterolytically cleaves hydrogen peroxide forming water and oxyferryl MPO (compound II). The two-electron oxidation reaction follows second-order kinetics with the apparent bimolecular rate constant being (6.8+/-0.6)x10(4)M(-1)s(-1) at pH 7.0. After depletion of (micromolar) H(2)O(2) compound II slowly decays to ferric MPO, whereas upon addition of millimolar H(2)O(2) to ferrous MPO, compound III (oxyperoxidase) is formed in a sequence of two reactions involving compound II formation and its direct reaction with H(2)O(2), which also follows second-order kinetics [(78+/-2)M(-1)s(-1) at pH 7.0]. It is discussed how these reactions contribute to the interconversion of compound II and compound III and could explain the catalase activity of MPO.
authors.affiliation: Institute of Chemistry, Metalloprotein Research Group, BOKU-University of Natural Resources and Applied Life Sciences, Muthgasse 18, A-1190 Vienna, Austria.
authors.forename: Walter
authors.initials: W
authors.lastname: Jantschko
authors.forename: Paul
authors.initials: P
authors.lastname: Georg Furtmüller
authors.forename: Martina
authors.initials: M
authors.lastname: Zederbauer
authors.forename: Martina
authors.initials: M
authors.lastname: Lanz
authors.forename: Christa
authors.initials: C
authors.lastname: Jakopitsch
authors.forename: Christian
authors.initials: C
authors.lastname: Obinger
mesh_terms: D000693:Anaerobiosis; D004789:Enzyme Activation; D005296:Ferrous Compounds / Q000737:chemistry*; D017022:Flow Injection Analysis; D006861:Hydrogen Peroxide / Q000737:chemistry*; D006997:Hypochlorous Acid / Q000737:chemistry*; D007124:Immunoenzyme Techniques; D007700:Kinetics; D010084:Oxidation-Reduction; D010100:Oxygen; D009195:Peroxidase / Q000138:chemical synthesis / Q000737:chemistry*; D013057:Spectrum Analysis
chemical_list: D005296:Ferrous Compounds; D006997:Hypochlorous Acid; D006861:Hydrogen Peroxide; D009195:Peroxidase; D010100:Oxygen