Eosinophil peroxidase
![Left: protoporphyrin IX. Right: modified form of heme cofactor released from peroxidase by protease digestion under nonreducing conditions.[5]](/Images/godic/202501/11/Eosinophil_peroxidase_-_Demonstration_of_protoporphyrin_linkage5956.gif")
![Active site of eosinophil peroxidase in the resting (reduced) state. Pictured: Proximal histidine-asparagine interaction (bottom); distal histidine and bound water (top). In the oxidized form, the oxyferryl radical takes the place of the bound solvent molecule, and the halide substrate binds alongside that. Not pictured: other bound solvent water molecules. Refer to PDB crystal structures or refs.[7] and.[5]](/Images/godic/202501/11/Active_site_of_eosinophil_peroxidase5956.gif")
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.