Eosinophil peroxidase
Encyclopedia
Eosinophil peroxidase is a haloperoxidase
enzyme
that in humans is encoded by the EPX gene
. The enzyme is a heterodimeric 71-77 kD peroxidase
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.
(such as, for example, the nematode worms involved in filariasis
); and also certain bacteria
(such as tuberculosis
bacteria). Eosinophil peroxidase is a haloperoxidase
that preferentially uses bromide over chloride for this purpose, generating hypobromite
(hypobromous acid
). The enzyme is also capable of oxidizing thiocyanate
(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.
Haloperoxidase
Haloperoxidases 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....
enzyme
Enzyme
Enzymes 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 gene
Gene
A 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 peroxidase
Peroxidase
Peroxidases 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 H2O2 formed by the eosinophil, and either chloride or bromide ions, eosinophil peroxidase provides a potent mechanism by which eosinophils kill multicellular parasitesParasitism
Parasitism 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 filariasis
Filariasis
Filariasis 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 bacteria
Bacteria
Bacteria 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 tuberculosis
Tuberculosis
Tuberculosis, 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 haloperoxidase
Haloperoxidase
Haloperoxidases 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 hypobromite
Hypobromite
The 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 acid
Hypobromous acid
Hypobromous 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 thiocyanate
Thiocyanate
Thiocyanate 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.