[Myeloperoxidase from neutrophil peroxisomes]

Peroxisomal myeloperoxidase plays a key role in synthesis of oxidants by neutrophilic leukocytes. This heme protein consists of two subunits connected by a disulfide bond. The enzyme uses H2O2 and Cl- for synthesis of HOCl--the major oxidant produced by neutrophils. Besides the chlorination reaction, myeloperoxidase exhibits some other properties depending on its oxidation state. The enzyme significantly affects synthesis of oxidants in the cells depending on the competing substrate concentrations and other factors. O2.- is also a physiological substrate of myeloperoxidase. Its reaction with the enzyme determines how the cells utilize O2.- for pathogen elimination. O2.- affects the chlorinating and peroxidase activities of myeloperoxidase. In addition, O2.- reacts with the enzyme yielding the catalytically active compound III that hydroxylates phenols.