Myeloperoxidase Information & Myeloperoxidase Links at HealthHaven.com

Myeloperoxidase
	; Myeloperoxidase drawn from PDB 1D7W.
Available structures
	1cxp, 1d2v, 1d5l, 1d7w, 1dnu, 1dnw, 1mhl, 1myp
Identifiers
Symbols	MPO;
External IDs	OMIM: 606989 MGI: 97137 HomoloGene: 55450 GeneCards: MPO Gene
Gene ontology
Molecular function	• chromatin binding; • peroxidase activity; • iron ion binding; • calcium ion binding; • oxidoreductase activity;
Cellular component	• nucleus; • lysosome;
Biological process	• anti-apoptosis; • defense response; • response to oxidative stress; • hydrogen peroxide catabolic process;
RNA expression pattern
	More reference expression data
Orthologs

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Myeloperoxidase (MPO) is a peroxidase enzyme (EC 1.11.1.7) most abundantly present in neutrophil granulocytes (a subtype of white blood cells). It is a lysosomal protein stored in azurophilic granules of the neutrophil. MPO has a heme pigment, which causes its green color in secretions rich in neutrophils, such as pus and some forms of mucus.

[edit] Structure

The 150-kDa MPO protein is a dimer consisting of two 15-kDa light chains and two variable-weight glycosylated heavy chains bound to a prosthetic heme group. Three isoforms have been identified, differing only in the size of the heavy chains^[1]. It contains a calcium binding site with 7 ligands, forming a pentagonal pyramid conformation. One of the ligands is the carbonyl group of Asp 96. Calcium-binding is important for structure of the active site because of Asp 96's close proximity to the catalytic His95 side chain.

[edit] Function

MPO produces hypochlorous acid (HOCl) from hydrogen peroxide (H₂O₂) and chloride anion (Cl^-) (or the equivalent from a non-chlorine halide) during the neutrophil's respiratory burst. It requires heme as a cofactor. Furthermore, it oxidizes tyrosine to tyrosyl radical using hydrogen peroxide as oxidizing agent.^[2]

Hypochlorous acid and tyrosyl radical are cytotoxic, so they are used by the neutrophil to kill bacteria and other pathogens.

[edit] Inhibitors of MPO

Azide has been used traditionally as an MPO inhibitor, but 4-ABH is a more specific inhibitor of MPO.

[edit] Genetics

The gene is located on chromosome 17 (17q23.1).

[edit] Role in disease

Myeloperoxidase deficiency is a hereditary deficiency of the enzyme, which predisposes to immune deficiency.^[3]

Antibodies against MPO have been implicated in various types of vasculitis, most prominently crescentic glomerulonephritis and Churg-Strauss syndrome. They are detected as perinuclear ANCAs (pANCAs), as opposed to the cytoplasmic ANCAs (cANCAs) against proteinase 3 (PR3), which are strongly associated with Wegener's granulomatosis.

[edit] Diagnostic use

Routine testing of MPO is not performed. A 2003 study suggested that it could serve as a sensitive predictor for myocardial infarction in patients presenting with chest pain.^[4] At present, PrognostiX Inc., run out of the Cleveland Clinic in Cleveland, Ohio, is the only company to have an FDA-approved ELISA test kit for MPO concentration. The product is known as CardioMPO and is used in clinical settings to triage patients who present chest pain. It operates using the sandwich ELISA method.

Immunohistochemical staining for myeloperoxidase used to be administered in the diagnosis of acute myeloid leukemia to demonstrate that the leukemic cells were derived from the myeloid lineage. However, the use of myeloperoxidase staining in this setting has been supplanted by the widespread use of flow cytometry. Myeloperoxidase staining is still important in the diagnosis of extramedullary leukemia, or chloroma.

[edit] See also

Chloroma

[edit] References

^ M Mathy-Hartert et al. (1998). "Purification of myeloperoxidase from equine polymorphonuclear leucocytes". Can J Vet Res. 62 (2): 127–132. PMID 9553712.
^ Heinecke JW, Li W, Francis GA, Goldstein JA. Tyrosyl radical generated by myeloperoxidase catalyzes the oxidative cross-linking of proteins. J Clin Invest 1993;91:2866-72. PMID 8390491.
^ Kutter D, Devaquet P, Vanderstocken G, Paulus JM, Marchal V, Gothot A. Consequences of total and subtotal myeloperoxidase deficiency: risk or benefit? Acta Haematol 2000;104:10-5. PMID 11111115.
^ Brennan M-L, Penn MS, Van Lente F, Nambi V, Shishehbor MH, Aviles RJ, Goormastic M, Pepoy ML, McErlean ES, Topol EJ, Nissen SE, Hazen SL. Prognostic value of myeloperoxidase in patients with chest pain. N Engl J Med 2003;349:1595-604. PMID 14573731.

[mathyhartert-0] M Mathy-Hartert et al. (1998). "Purification of myeloperoxidase from equine polymorphonuclear leucocytes". Can J Vet Res. 62 (2): 127–132. PMID 9553712.

[1] Heinecke JW, Li W, Francis GA, Goldstein JA. Tyrosyl radical generated by myeloperoxidase catalyzes the oxidative cross-linking of proteins. J Clin Invest 1993;91:2866-72. PMID 8390491.

[2] Kutter D, Devaquet P, Vanderstocken G, Paulus JM, Marchal V, Gothot A. Consequences of total and subtotal myeloperoxidase deficiency: risk or benefit? Acta Haematol 2000;104:10-5. PMID 11111115.

[3] Brennan M-L, Penn MS, Van Lente F, Nambi V, Shishehbor MH, Aviles RJ, Goormastic M, Pepoy ML, McErlean ES, Topol EJ, Nissen SE, Hazen SL. Prognostic value of myeloperoxidase in patients with chest pain. N Engl J Med 2003;349:1595-604. PMID 14573731.

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