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.
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.
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.
|Haloperoxidase||Oxidisable halide||Origin, Notes|
|Chloroperoxidase (CPO)||Cl–, Br–, I–||neutrophils (myeloperoxidase),
|Bromoperoxidase (BPO)||Br–, I–||milk, saliva, tears (lactoperoxidase),
|Iodoperoxidase (IPO)||I–||horseradish (horseradish peroxidase)
- S.L. Neidleman, J. Geigert (1986) Biohalogenation - principles, basic roles and applications; Ellis Horwood Ltd Publishers; Chichester; ISBN 0-85312-984-3
-  Eosinophils preferentially use bromide to generate halogenating agents - Mayeno et al. 264 (10): 5660 - Journal of Biological Chemistry
-  Role of Heme-Protein Covalent Bonds in Mammalian Peroxidases
- PMID 19363038 Review of vanadium-dependent bromoperoxidases in nature