Haloperoxidase
Haloperoxidases are peroxidases that are able to mediate the oxidation of halides by hydrogen peroxide.[1] 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.[2]
The mammalian haloperoxidases myeloperoxidase (MPO), lactoperoxidase (LPO) and eosinophil 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.[3]
A specific vanadium bromoperoxidase in marine organisms (fungi, bacteria, microalgae, perhaps other eukaryotes) uses vanadate and hydrogen peroxide to brominate electrophilic organics.[4]
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.
Haloperoxidase | Oxidisable halide | Origin, Notes |
---|---|---|
Chloroperoxidase (CPO) | Cl−, Br−, I− | neutrophils (myeloperoxidase), eosinophils (eosinophil peroxidase, can use Cl−, prefers Br−) |
Bromoperoxidase (BPO) | Br−, I− | milk, saliva, tears (lactoperoxidase), sea urchin eggs (), |
Iodoperoxidase (IPO) | I− | horseradish (horseradish peroxidase) |
See also[]
References[]
- ^ S.L. Neidleman, J. Geigert (1986) Biohalogenation - principles, basic roles and applications; Ellis Horwood Ltd Publishers; Chichester; ISBN 0-85312-984-3
- ^ [1] Eosinophils preferentially use bromide to generate halogenating agents - Mayeno et al. 264 (10): 5660 - Journal of Biological Chemistry
- ^ [2] Role of Heme-Protein Covalent Bonds in Mammalian Peroxidases
- ^ Winter, JM; Moore, BS (July 2009). "Exploring the chemistry and biology of vanadium-dependent haloperoxidases". J. Biol. Chem. 284 (28): 18577–81. doi:10.1074/jbc.R109.001602. PMC 2707250. PMID 19363038.
- EC 1.11.1