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Mechanism of reaction of myeloperoxidase with nitrite

U Burner1, P G Furtmuller, A J Kettle

  • 1Institute of Chemistry, University of Agricultural Sciences, Muthgasse 18, A-1190 Vienna, Austria.

The Journal of Biological Chemistry
|April 25, 2000
PubMed

Insights

Myeloperoxidase (MPO) utilizes nitrite as a substrate in its enzymatic cycle, particularly during inflammatory conditions. This study elucidates the reaction kinetics and pH dependence of MPO with nitrite.

Area of Science:

  • Biochemistry
  • Enzymology
  • Inflammation Research

Background:

  • Myeloperoxidase (MPO) is a key neutrophil protein implicated in inflammatory diseases.
  • Tyrosine nitration is observed in inflammatory conditions involving neutrophil and macrophage activation.
  • The role of nitrite as a physiological substrate for MPO remains unclear.

Purpose of the Study:

  • To investigate the reaction kinetics of MPO with nitrite.
  • To determine if nitrite is a physiological substrate for MPO.
  • To elucidate the pH dependence of MPO-nitrite interactions.

Main Methods:

  • Sequential mixing stopped-flow analysis was employed.
  • Reactions of ferric MPO, compound I, and compound II with nitrite were studied.
  • Experiments were conducted across a pH range of 4-8 at 15°C.

Main Results:

  • MPO forms a low-spin complex with nitrite, with varying rates and dissociation constants at different pH values.
  • Nitrite is oxidized by MPO through two one-electron steps.
  • Rate constants for the reduction of MPO intermediates (Compound I and II) by nitrite were determined and showed pH dependence.

Conclusions:

  • Nitrite is a physiological substrate for MPO, undergoing oxidation within the MPO peroxidase cycle.
  • The pH dependence suggests a catalytic residue (likely distal histidine) with a pKa of ~4.3 is crucial for nitrite binding and oxidation.
  • These findings contribute to understanding MPO's role in inflammatory processes involving tyrosine nitration.

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