Eosinophil peroxidase is a
haloperoxidaseHaloperoxidases are peroxidases that are able to mediate the oxidation of halides by hydrogen peroxide. Both halides and hydrogen peroxide are widely available in the environment....
enzymeEnzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
that in humans is encoded by the
EPX geneA gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
. The enzyme is a heterodimeric 71-77 kD
peroxidasePeroxidases are a large family of enzymes that typically catalyze a reaction of the form:For many of these enzymes the optimal substrate is hydrogen peroxide, but others are more active with organic hydroperoxides such as lipid peroxides...
consisting of a heavier glycosylated chain and a lighter nonglycosylated chain. This enzyme prefers bromide over chloride as a substrate, converting it to toxic hypobromite.
Function
In the presence of H
2O
2 formed by the eosinophil, and either chloride or bromide ions, eosinophil peroxidase provides a potent mechanism by which eosinophils kill multicellular
parasitesParasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...
(such as, for example, the nematode worms involved in
filariasisFilariasis is a parasitic disease and is considered an infectious tropical disease, that is caused by thread-like nematodes belonging to the superfamily Filarioidea, also known as "filariae"....
); and also certain
bacteriaBacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
(such as
tuberculosisTuberculosis, MTB, or TB is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis usually attacks the lungs but can also affect other parts of the body...
bacteria). Eosinophil peroxidase is a
haloperoxidaseHaloperoxidases are peroxidases that are able to mediate the oxidation of halides by hydrogen peroxide. Both halides and hydrogen peroxide are widely available in the environment....
that preferentially uses bromide over chloride for this purpose, generating
hypobromiteThe hypobromite ion, also called alkaline bromine water, is BrO−. Bromine is in the +1 oxidation state. Hypobromite is the bromine compound analogous to hypochlorites found in common bleaches, and in immune cells...
(
hypobromous acidHypobromous acid is a weak, unstable acid with chemical formula HBrO. It is also called bromic acid, bromanol or hydroxidobromine. It occurs only in solution and has chemical and physical properties that are very similar to those of hypochlorous acid.In aqueous solution, hypobromous acid partially...
). The enzyme is also capable of oxidizing
thiocyanateThiocyanate is the anion [SCN]−. It is the conjugate base of thiocyanic acid. Common derivatives include the colourless salts potassium thiocyanate and sodium thiocyanate. Organic compounds containing the functional group SCN are also called thiocyanates...
(SCN-) and uses it as a co-substrate, with optimal concentrations occurring at about normal plasma levels.
Eosinophil peroxidase is also partly responsible for tissue remodeling.
Role in pathology
The oxidizing compounds produced by eosinophil peroxidase have been implicated in the inflammatory pathology of several disease states, including asthma.
External links
From JC Segen Dictionary of Modern Medicine database