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 oxidise 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 oxidised by hydrogen peroxide. The table shows the classification of haloperoxidases according to the halides which oxidation they are able to catalyse.
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]
| Haloperoxidase | Oxidisable halide | Origin |
|---|---|---|
| Chloroperoxidase (CPO) | Cl–, Br–, I– | neutrophils (myeloperoxidase), eosinophils (eosinophil peroxidase), |
| Bromoperoxidase (BPO) | Br–, I– | milk, saliva, tears (lactoperoxidase), sea urchin eggs (ovoperoxidase), |
| Iodoperoxidase (IPO) | I– | horseradish (horseradish peroxidase) |
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
See also
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