Myeloperoxidase is a peroxidase enzyme that is part of the host defense system of polymorphonuclear leukocytes. The gene for MPO was cloned independently from several laboratories. A decrease in MPO expression was noticed upon differentiation of HL-60 cells. MPO catalyzes the reaction of hydrogen peroxide and chloride to produce hypochlorous acid and other potent antimicrobial oxidants. Knockout mice of MPO are impaired in clearing select microbial infections. Processing of mature MPO from an initial 80-90 kDa translation product involves insertion of a heme moiety, glycosylation, and proteolytic cleavage. The mature protein is a tetramer of two heavy chains and two light chains. It is abundantly expressed in neutrophils and monocytes and secreted during their activation. Heightened MPO levels have been associated with tissue damage and a number of pathological conditions.
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