title: Inactivation of human myeloperoxidase by hydrogen peroxide.
abstract: Human myeloperoxidase (MPO) uses hydrogen peroxide generated by the oxidative burst of neutrophils to produce an array of antimicrobial oxidants. During this process MPO is irreversibly inactivated. This study focused on the unknown role of hydrogen peroxide in this process. When treated with low concentrations of H2O2 in the absence of reducing substrates, there was a rapid loss of up to 35% of its peroxidase activity. Inactivation is proposed to occur via oxidation reactions of Compound I with the prosthetic group or amino acid residues. At higher concentrations hydrogen peroxide acts as a suicide substrate with a rate constant of inactivation of 3.9 × 10(-3) s(-1). Treatment of MPO with high H2O2 concentrations resulted in complete inactivation, Compound III formation, destruction of the heme groups, release of their iron, and detachment of the small polypeptide chain of MPO. Ten of the protein's methionine residues were oxidized and the thermal stability of the protein decreased. Inactivation by high concentrations of H2O2 is proposed to occur via the generation of reactive oxidants when H2O2 reacts with Compound III. These mechanisms of inactivation may occur inside neutrophil phagosomes when reducing substrates for MPO become limiting and could be exploited when designing pharmacological inhibitors.
authors.affiliation: Centre for Free Radical Research, University of Otago Christchurch, Christchurch, New Zealand; Department of Chemistry, Division of Biochemistry, BOKU - University of Natural Resources and Life Sciences, Muthgasse 18, Vienna, Austria.
authors.forename: Martina
authors.initials: M
authors.lastname: Paumann-Page
authors.forename: Paul G
authors.initials: PG
authors.lastname: Furtmüller
authors.forename: Stefan
authors.initials: S
authors.lastname: Hofbauer
authors.forename: Louise N
authors.initials: LN
authors.lastname: Paton
authors.forename: Christian
authors.initials: C
authors.lastname: Obinger
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Kettle
mesh_terms: D004789:Enzyme Activation / Q000187:drug effects; D004795:Enzyme Stability / Q000187:drug effects; D006418:Heme / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007700:Kinetics; D009195:Peroxidase / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D017433:Protein Structure, Secondary / Q000187:drug effects; D017434:Protein Structure, Tertiary / Q000187:drug effects; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D058767:Protein Unfolding / Q000187:drug effects; D013696:Temperature
chemical_list: D021122:Protein Subunits; D006418:Heme; D006861:Hydrogen Peroxide; D009195:Peroxidase
keywords: Mechanism-based inhibition; Myeloperoxidase; Neutrophils; Oxidative modification; Oxidative stress; Suicide inhibitor
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