Analysis of the peptide subunits of human neutrophil myeloperoxidase

Myeloperoxidase is a cationic protein present in the azurophilic granules of human neutrophils and constitutes 2% to 5% of neutrophil protein by weight. Despite extensive characterization of the functional importance of myeloperoxidase in the microbicidal activity of neutrophils, there is no consensus regarding the subunit composition of this enzyme or the presence of genetic polymorphism. Using isoelectric focussing and peptide mapping of chymotryptic digests of myeloperoxidase subunits under reducing and nonreducing conditions, we found two different heavy chain peptides that have overlapping but distinctive chymotryptic digest maps. One of these heavy chains has a reducible intrapeptide disulfide bond not found in the other. These results suggest that the model proposed for the structure of myeloperoxidase as a symmetric molecule with two identical heavy-light protomers may not be correct.