View source for Myeloperoxidase

{{protein
| Name = myeloperoxidase
| caption = Myeloperoxidase drawn from {{PDB|1D7W}}.
| image = Myeloperoxidase.png
| width = 176
| HGNCid = 7218
| Symbol = MPO
| AltSymbols = 
| EntrezGene = 4353
| OMIM = 606989
| RefSeq = NM_000250
| UniProt = P05164
| PDB = 
| ECnumber = 1.11.1.7
| Chromosome = 17
| Arm = q
| Band = 21.3
| LocusSupplementaryData = -q23
}}
'''Myeloperoxidase''' (MPO) is a [[peroxidase]] [[enzyme]] ({{EC number|1.11.1.7}}) most abundantly present in [[neutrophil granulocyte]]s (a subtype of [[white blood cell]]s). It is a [[lysosome|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]].

==Function==
MPO produces [[hypochlorous acid]] (HOCl) from [[hydrogen peroxide]] (H<sub>2</sub>O<sub>2</sub>) and [[chloride]] [[anion]] (Cl<sup>-</sup>) 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.<ref>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.</ref>

Hypochlorous acid and tyrosyl radical are [[cytotoxic]], so they are used by the neutrophil to kill [[bacteria]] and other [[pathogen]]s.

==Genetics==
The [[gene]] is located on [[chromosome]] 17 (17q23.1).

==Role in disease==
[[Myeloperoxidase deficiency]] is a rare hereditary deficiency of the enzyme, which predisposes to [[immune deficiency]].<ref>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.</ref> 

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

==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]].<ref>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.</ref> Currently, 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 that present chest pain. It operates using the sandwich ELISA method.

Historically, [[immunohistochemistry|immunohistochemical]] staining for myeloperoxidase was used in the diagnosis of [[acute myeloid leukemia]] to demonstrate that the leukemic cells were derived from the [[myeloid]] lineage. However, more recently, 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]].

==References==
<references/>

==See also==
*[[Chloroma]]

{{Peroxidases}}
[[Category:EC 1.11.1]]
[[Category:Hemoproteins]]

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[[fr:Myéloperoxidase]]
[[ru:Миелопероксидаза]]
[[zh:过氧化物酶]]