Myeloperoxidase (MPO) is a peroxidase enzyme (EC 1.11.1.7) 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 catalyzes the production of hypochlorous acid (HClO) from hydrogen peroxide (H?O?) and chloride anion (Cl-, or the equivalent from a non-chlorine halide). MPO also oxidizes tyrosine to a tyrosyl radical using hydrogen peroxide as an oxidizing agent. In BioVision's MPO Assay Kit, the HClO produced from H?O? and Cl- is reacted with taurine to generate the taurine chloramine, which subsequently reacts with the TNB2- probe t