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Haloperoxidases are peroxidases that are able to mediate the oxidation of halides by hydrogen peroxide.〔S.L. Neidleman, J. Geigert (1986) Biohalogenation - principles, basic roles and applications; Ellis Horwood Ltd Publishers; Chichester; ISBN 0-85312-984-3〕 Both halides and hydrogen peroxide are widely available in the environment. The Nernst equation shows that hydrogen peroxide can oxidize chloride (E°= 1.36 V), bromide (E°= 1.09 V) and iodide (E°= 0.536 V) from a thermodynamic perspective under natural conditions, i.e., a temperature range of about 0-30 °C and a pH ranging from about 3 (humic soil layer) to about 8 (sea water). Fluoride (E°= 2.87 V) cannot be oxidized by hydrogen peroxide. ==Classification== The table shows the classification of haloperoxidases according to the halides whose oxidation they are able to catalyze. The classification of these enzymes by substrate-usability does not necessarily indicate enzyme substrate ''preference.'' For example, although eosinophil peroxidase is ''able'' to oxidize chloride, it preferentially oxidizes bromide.〔() Eosinophils preferentially use bromide to generate halogenating agents - Mayeno et al. 264 (10): 5660 - Journal of Biological Chemistry〕 The mammalian haloperoxidases myeloperoxidase (MPO), lactoperoxidase (LPO) and eosoniphil peroxidase (EPO) are also capable of oxidizing the pseudohalide thiocyanate (SCN−). They each contain a heme prosthetic group covalently bound by two ester linkages to aspartate and/or glutamate side-chains. MPO has a third covalent link through a methionine residue. Horseradish peroxidase is also capable of oxidizing these substrates, but its heme is not covalently bound and becomes damaged during turnover.〔() Role of Heme-Protein Covalent Bonds in Mammalian Peroxidases〕 A specific vanadium bromoperoxidase in marine organisms (fungi, bacteria, microalgae, perhaps other eukaryotes) uses vanadate and hydrogen peroxide to brominate electrophilic organics.〔PMID 19363038 Review of vanadium-dependent bromoperoxidases in nature〕 Murex snails have a bromoperoxidase used to produce Tyrian purple dye. The enzyme is very specific to bromide and physically stable, but has not been characterized as to its active site. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Haloperoxidase」の詳細全文を読む スポンサード リンク
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