Résumé : Myeloperoxidase (MPO, E.C. is a heme-containing glycosylated oxidoreductase that catalyses the production of hypochlorous acid (HOCl) in the presence of hydrogen peroxide (H2O2) and chloride anions. Besides its well studied catalytic activity, the role of its overall structure and glycosylation pattern in biological function is barely known. Here, the N-glycan composition of native dimeric human MPO purified from neutrophils and of monomeric MPO recombinantly expressed in Chinese hamster ovary cells has been investigated by mass spectrometry. Analyses showed for the first time the presence of five N-glycans at positions 323, 355, 391, 483, 729 in both proteins. Site by site analysis demonstrated a well conserved micro- and macro-heterogeneity and more complex-type N-glycans for the recombinant form. Moreover, a comparison of biological functionality of glycosylated and deglycosylated recombinant MPO has been investigated in three different in vitro model. These data suggest for the first time that N-glycosylation is required for the optimal activity of a peroxidase such as myeloperoxidase. Data are also discussed with regard to biosynthesis and three-dimensional structure of MPO