Neuraminidase activity in human leukocytes

Abstract Leukocytes isolated from human blood contain neuraminidase activity. This enzyme has a pH optimum of 4.0, and it is present in the sedimentable fraction of leukocyte homogenates. Ca 2+ , Mg 2+ , Cu 2+ , and Zn 2+ at 1mM concentration do not cause any significant changes of enzyme activity, while Hg 2+ , at the same concentration, is clearly inhibitory. This enzyme is also inhibited by Triton X-100, by deoxycholate, and by isotonic concentrations of NaCl, KCl, LiCl, and CaCl 2 . Low molecular weight substrates such as neuramin-lactose, neuramin-lactose sulfate, and sialoglycopeptides are hydrolyzed at a higher rate than gangliosides and glycoproteins. A procedure for the determination of leukocyte neuraminidase for clinical purposes has been developed, and the normal levels of enzyme activity have been established in blood from healthy, human adult subjects.