Myeloperoxidase, Neutrophil (MPO) Enzyme

Myeloperoxidase (MPO) is a heme protein synthesized during myeloid differentiation that constitutes the major component of neutrophil azurophilic granules. Produced as a single chain precursor, myeloperoxidase is subsequently cleaved into a light and heavy chain. The mature myeloperoxidase is a tetramer composed of 2 light chains and 2 heavy chains. This enzyme produces hypohalous acids central to the microbicidal activity of netrophils. [provided by RefSeq, Jul 2008]

Function: Part of the host defense system of polymorphonuclear leukocytes. It is responsible for microbicidal activity against a wide range of organisms. In the stimulated PMN, MPO catalyzes the production of hypohalous acids, primarily hypochlorous acid in physiologic situations, and other toxic intermediates that greatly enhance PMN microbicidal activity.

Catalytic activity: Cl- + H2O2 + H+ = HClO + H2O.Cl- + H2O2 = HOCl + 2 H2O.

Cofactor: Binds 1 calcium ion per monomer.Binds 1 heme B (iron-protoporphyrin IX) group covalently per monomer.

Subunit structure: Homodimer; disulfide-linked. Each monomer consists of a light and a heavy chain. Ref.13 Ref.21

Subcellular location: Lysosome.

Involvement in disease: Myeloperoxidase deficiency (MPOD) [MIM:254600]: A disorder characterized by decreased myeloperoxidase activity in neutrophils and monocytes that results in disseminated candidiasis.Note: The disease is caused by mutations affecting the gene represented in this entry. Ref.24 Ref.25 Ref.26 Ref.27 Ref.28

Sequence similarities: Belongs to the peroxidase family. XPO subfamily.