Inactivation of human myeloperoxidase by hydrogen peroxide

Arch Biochem Biophys. 2013 Nov 1;539(1):51-62. doi: 10.1016/j.abb.2013.09.004. Epub 2013 Sep 11.

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.

Keywords: Mechanism-based inhibition; Myeloperoxidase; Neutrophils; Oxidative modification; Oxidative stress; Suicide inhibitor.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Enzyme Activation / drug effects
  • Enzyme Stability / drug effects
  • Heme / chemistry
  • Heme / metabolism
  • Humans
  • Hydrogen Peroxide / pharmacology*
  • Kinetics
  • Peroxidase / antagonists & inhibitors
  • Peroxidase / chemistry*
  • Peroxidase / metabolism*
  • Protein Structure, Secondary / drug effects
  • Protein Structure, Tertiary / drug effects
  • Protein Subunits / chemistry
  • Protein Subunits / metabolism
  • Protein Unfolding / drug effects
  • Temperature

Substances

  • Protein Subunits
  • Heme
  • Hydrogen Peroxide
  • Peroxidase