Myeloperoxidase interaction with peroxynitrite: chloride deficiency and heme depletion

Semira Galijasevic, Dhiman Maitra, Tun Lu, Inga Sliskovic, Ibrahim Abdulhamid, Husam M. Abu-Soud

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24 Scopus citations


Myeloperoxidase (MPO) is a hemoprotein involved in the leukocyte-mediated defense mechanism and uses hydrogen peroxide (H2O2) and chloride (Cl-) to produce hypochlorous acid. In human saliva and in hypochloremic alkalosis syndrome occurring in breast-fed infants, the MPO-H2O2 system functions in a lower Cl- concentration (10-70 mM) compared to plasma levels (100 mM) as part of the antibacterial defense system. The impact of low Cl- concentration and exposure to high peroxynitrite (ONOO-) synthesized from cigarette smoke or oxidative stress on MPO function is still unexplored. Rapid mixing of ONOO- and MPO caused immediate formation of a transient intermediate MPO Compound II, which then decayed to MPO-Fe(III). Double mixing of MPO with ONOO- followed by H2O2 caused immediate formation of Compound II, followed by MPO heme depletion, a process that occurred independent of ONOO- concentration. Peroxynitrite/H2O2-mediated MPO heme depletion was confirmed by HPLC analysis, and in-gel heme staining showing 60-70% less heme content compared to the control. A nonreducing denaturing SDS-PAGE showed no fragmentation or degradation of protein. Myeloperoxidase heme loss was completely prevented by preincubation of MPO with saturating amounts of Cl-. Chloride binding to the active site of MPO constrains ONOO- binding by filling the space directly above the heme moiety or by causing a protein conformational change that constricts the distal heme pocket, thus preventing ONOO- from binding to MPO heme iron. Peroxynitrite interaction with MPO may serve as a novel mechanism for modulating MPO catalytic activity, influencing the regulation of local inflammatory and infectious events in vivo.

Original languageEnglish
Pages (from-to)431-439
Number of pages9
JournalFree Radical Biology and Medicine
Issue number4
StatePublished - Aug 15 2009


  • Free radicals
  • Hydrogen peroxide
  • Hypohalous acid
  • Inflammation
  • Mammalian peroxidase
  • Smoking


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