Eosinophil Peroxidase (EPX)

Eosinophil peroxidase is a haloperoxidase enzyme 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. 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 parasites (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.