Jpn. J. Infect. Dis., 57, S31-S33, 2004
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Reactions of Superoxide with Myeloperoxidase
and Its Products
Christine C. Winterbourn* and Anthony J. Kettle
Free Radical Research, Department of Pathology, Christchurch
School of Medicine and Health Sciences, Christchurch, New Zealand
*Corresponding author: christine.winterbourn@chmeds.ac.nz
SUMMARY: Myeloperoxidase (MPO) uses hydrogen peroxide to oxidize
chloride to hypochlorous acid. It also converts numerous substrates
to reactive free radicals. When released by neutrophils, the enzyme
operates in the presence of a flux of superoxide. We show that
superoxide has a profound influence on oxidative reactions catalysed
by MPO. It reacts directly with the enzyme to modulate production
of hypochlorous acid. Within neutrophil phagosomes, where MPO
functions to kill micro-organisms, it may be the preferred substrate
for the enzyme. Superoxide also reacts rapidly with radicals generated
by MPO, e.g. from tyrosine and tyrosyl peptides. Initial products
are organic peroxides. These species are likely to be toxic and
contribute to the pathophysiological actions of MPO.