Eosinophil peroxidase

Eosinophil peroxidase is an enzyme found within the eosinophil granulocytes, innate immune cells of humans and mammals. This oxidoreductase protein is encoded by the gene EPX, expressed within these myeloid cells. EPO shares many similarities with its orthologous peroxidases, myeloperoxidase (MPO), lactoperoxidase (LPO), and thyroid peroxidase (TPO). The protein is concentrated in secretory granules within eosinophils. Eosinophil peroxidase is a heme peroxidase, its activities including the oxidation of halide ions to bacteriocidal reactive oxygen species, the cationic disruption of bacterial cell walls, and the post-translational modification of protein amino acid residues. The major function of eosinophil peroxidase is to catalyze the formation of hypohalous acids from hydrogen peroxide and halide ions in solution. For example: H2O2 + Br− → HOBr + H2O Hypohalous acids formed from halides or pseudohalides are potent oxidizing agents. However, the role of eosinophilic peroxidase seems to be to generate hyphalous acids largely from bromide and iodide rather than chloride, since the former are favored greatly over the latter. The enzyme myeloperoxidase is responsible for formation of most of the hypochlorous acid in the body, and eosinophil peroxidase is responsible for reactions involving bromide and iodide.