Myeloperoxidase (MPO) is a peroxidase enzyme most abundantly expressed in neutrophil granulocytes. It is a lysosomal protein stored in the azurophilic granules of the neutrophil. MPO contains a heme pigment which causes its green color in secretions rich in neutrophils, such as pus and some forms of mucus. MPO catalyses the production of hypochlorous acid (HClO) from hydrogen peroxide (H₂O₂) and chloride anion (Cl-, or the equivalent from a non-chlorine halide). MPO also oxidises tyrosine to a tyrosyl radical using hydrogen peroxide as an oxidising agent. BioVision’s Myeloperoxidase ELISA kit is a sandwich ELISA assay for the quantitative measurement of MPO in Human serum, plasma and cell culture supernatants. The density of color is proportional to the amount of MPO captured from the samples.