Myeloperoxidase

In contrast to MPO, eosinophil peroxidase (EPO) prefers to oxidize plasma level bromide (20-100 pM) to hypobromous acid (HOBr) and several biological targets are implicated, including nucleic acids and nucleosides (1480, 1482, 2376), proteins (1812, 1813, 2377, 2378), unsaturated fatty acids (2379), and low-density lipoprotein (2380, 2381). This EPO-dependent bromination is suggested to be involved in the pathogenesis of asthma (2382). Accordingly, both 3-bromotyrosine and 3,5-dibromotyrosine (1812,1813) are produced by EPO-induced bromination of tyrosine residues in lung tissue (1813, 2382). 

The question posed by Winterton in 1997, Are Organochlorine Compounds Created in the Human Body (2383), can now be answered with an authoritative 

1 Lactoperoxidase. Present in milk and saliva, LPO plays a role in the prevention of bacterial growth. In the compound I, the radical centre undergoes transferral from the porphyrin to the protein moiety. The resultant protein radical can react with other proteins. Thus, freeze-quench EPR has permitted the detection of protein radicals from P-microglobulin, casein and albumin. Radicals have also been observed following the activation of LPO in milk.  

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Recendy, the myelotoxicity has been proposed to occur through initial conversion of benzene to phenol and hydroquinone in the fiver, selective accumulation of hydroquinone in the bone marrow, followed by conversion of hydroquinone to benzoquinone via bone marrow myeloperoxidase. Benzoquinone is then proposed to react with macromolecules dismpting cellular processes (108). 

According to Reichl et al. (2000), the oxidation of pholasin by compound I or II of horseradish peroxidase induces an intense light emission, whereas native horseradish peroxidase shows only a small effect. The luminescence of pholasin by native myeloperoxidase (verdoperoxidase) is diminished by preincubation with catalase, which is interpreted as the result of the removal of a trace amount of naturally occurring H2O2 in the buffer (about 10-8 M) that forms compound I... 

These stimuli elicit a complex series of responses that result in cell functions such as chemotaxis and release of inflammatory compounds, oxidants, and proteases. Probably related to chemotaxis is a rapid, transient actin polymerization response. Inflammation results in part from the release of proteases and myeloperoxidase normally stored in granules inside the cell (5) and from oxidants produced by an NADPH-oxidase system (6) located primarily... 

Contain certain unique enzymes (eg, myeloperoxidase and NADPH-oxidase) and proteins... 

Neutrophils Contain Myeloperoxidase, Which Catalyzes the Production of Chlorinated Oxidants... 

The enzyme myeloperoxidase, present in large amounts in neutrophil granules and responsible for the green color of pus, can act on HjOj to produce hypohalous acids ... 

Allegra, M. et al.. Mechanism of interaction of betanin and indicaxanthin with human myeloperoxidase and hypochlorons acid, Biochem. Biophys. Res. Commun., 332, 837, 2005. 

Brennan M-L and et al. (2002) A tale of two controversies. Defining both the role of peroxidases in nitrotyro-sine formation in vivo using eosinophil peroxidase and myeloperoxidase-deficient mice, and the natnre of the peroxidase-generated reactive nitrogen species. J Biol Chem 277 17415-17427. 

The effect of gold compounds on human neutrophil myeloperoxidase, in Bioinorganic Chemistry of Gold Coordination Compounds (eds B.M. Sutton and R.G. Franz), SK F, Philadelphia, pp. 58-66. 

Beverly, B. and Couri, D. (1987) Role of Myeloperoxidase (MPO) in Aurothiomalate Metabolism. Federation Proceedings, 46, 854. 

Grisham, M.B., Ryan, E. and Von Ritter, C. (1987). 5-Aminosalicylic acid scavenges hydroxyl radical and inhibits myeloperoxidase activity. Gastroenterology 92, 1416. 

Polymorphonuclear leucocytes (PMNs) employ a system comprising myeloperoxidase, hydrogen peroxide, and a halide factor to kill microorganisms and tumour cells. This process is sometimes loosely called the respiratory burst , which refers to the sudden rise in oxygen consumption by the phagocytosing neutrophils that is independent of the mitochondrial electron transport chain. 

The plant is strongly aromatic on account of an essential oil which comprises cis-a-ocimene (25.11%), 3,7-dimethyl-l,6-octadien-3 ol (16.85%), and trans-nerolidol (13.89%), hence the use of the plant in aromatherapy. A methanolic extract of bark of Litsea cubeba (Lour.) Pers. and its fractions (0.01 mg/mL) from bark inhibit NO and PGE2 production in LPS-activated RAW 264.7 macrophages without significant cytotoxicity at less than 0.01 mg/mL concentration. The methanol extract decreased the enzymatic activity of myeloperoxidase (0.05 mg/mL). These findings suggest that L. cubeba is beneficial for inflammatory conditions and may contain compound(s) with anti-inflammatory properties (63). Can we expect the vasorelaxant laurotetanine (64) isolated from the plant to exert such activity ... 

Melatonin can be metabolized non-enzymatically in all cells, and extra-cellularly by free radicals and a few other oxidants. It is converted into cyclic 3-hydroxymelatonin when it directly scavenges two hydroxyl radicals (Tan et al. 1998). In the brain, a substantial fraction of melatonin is metabolized to kynuramine derivatives (Hirata et al. 1974). AFMK is produced by numerous non-enzymatic and enzymatic mechanisms (Hardeland et al. 2006) its formation by myeloperoxidase appears to be important in quantitative terms (Ferry et al. 2005). 

Ferry, G., Ubeaud, C., Lambert, P. H. et at (2005). Molecular evidence that melatonin is enzymatically oxidized in a different manner than tryptophan. Investigation on both indoleamine-2,3-dioxygenase and myeloperoxidase. Biochem.J. 388, 205-15. 

Kagan, V.E. et al. (2010) Carbon nanotubes degraded by neutrophil myeloperoxidase induce less pulmonary inflammation. Nature Nanotechnology,... 

In neutrophils the presence of myeloperoxidase, MPO, within the granules will catalyse the formation of hypochlorous acid from the reaction between hydrogen peroxide and chloride ions while eosinophils MPO preferentially use Br- ions. 

Cramer, E.M., Beesley, J.E., Pulford, K.A.F., Breton-Gorius, J., and Mason, D.Y. (1989) Colocalization of elastase and myeloperoxidase in human blood and bone marrow neutrophils using a monoclonal antibody and immunogold. Am. J. Pathol. 134, 1275-1284. 

Winterbourn, C.C., and Kettle, A.J. (2000) Biomarkers of myeloperoxidase-derived hypochlorous acid. Free Radic. Biol. Med. 29, 403-409. 

T. Odajima and I. Yamazaki, Myeloneperoxidase of the leukocyte of normal blood. 3. The reaction of ferric myeloperoxidase with superoxide anion. Biochim. Biophys. Acta. 284, 355-359 (1972). 

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