The function of EPX (eosinophil peroxidase, ENSG00000121053) is as follows. Heme-containing oxidoreductase that catalyzes the oxidation of small anions, such as nitrite, halides (e.g bromide and chloride (at pH 6.5)) and pseudohalides (e.g thiocyanate) by using hydrogen peroxide to generate the corresponding reactive species hypobromite, hypochlorite, hypothiocyanous acid, and nitrogen dioxide (PubMed:11013238, PubMed:11112545, PubMed:12540536, PubMed:7852368). Also oxidizes thiocyanate (SCN(-)) to cyanate (OCN(-)) (PubMed:11112545). Functionally involved in inflammatory responses and exhibits antimicrobial activity (PubMed:12540536, PubMed:27587397). Can also oxidize amino acid residues on proteins and generate bromination, nitration and carbamoylation post-translational modifications, respectively (PubMed:18694936, PubMed:27587397). Mediates the nitration of tyrosine (3-nitrotyrosine) which is only observed in secondary granule proteins in mature resting eosinophils in the presence of the cosubstrates, hydrogen peroxide and nitrite (PubMed:18694936). Mediates oxidation of tyrosine residues on proteins in eosinophils to form brominating species, 3-bromotyrosine and 3, 5-dibromotyrosine in the presence of hydrogen peroxide and bromide (By similarity). Promotes protein carbamoylation at sites of inflammation during asthma by using thiocyanate and hydrogen peroxide to form cyanate which carbamoylates lysine residues to form homocitrulline (PubMed:27587397). {ECO:0000250|UniProtKB:P80550, ECO:0000269|PubMed:11013238, ECO:0000269|PubMed:11112545, ECO:0000269|PubMed:12540536, ECO:0000269|PubMed:18694936, ECO:0000269|PubMed:27587397, ECO:0000269|PubMed:7852368}.