Activities and specificities of N-acetylneuraminyltransferases in leukemic cells.

Recently, interest in glycosyltransferases has increased due to the finding that differentiation and neoplastic transformation of cells may be accompanied by alterations in the composition and metabolism of cellular glycoconjugates. Previous studies using lactose as exogenous acceptor have shown apparent differences in the expression of the activities of fucosyland N-acetylneuraminyltransferases in various leukemic cells arrested at different stages of cell maturation [I]. The aim of this study was to determine the activities and linkage specifities of different N-acetylneuraminyltransferases in various leukemic and normal cell populations. Normal and leukemic cells were isolated from human blood by differential and/or gradient centrifugation and characterized by surface membrane marker analysis as described recently [I]. N-acetylneuraminyl (Neu Ac) transferase activites were assayed in cell lysates by measuring the transfer of [14C] NeuAc from CMP-[14C]NeuAc to different exogenous glycoprotein acceptors. The reaction mixture for the standard N-acetylneuraminyltransferase assay contained 50 p1 lysate (108 sonicated cells or platelets/ml of 0.05 M HEPES-buffer, pH 6.8, containing 0.1% Triton X100), 100 pl acceptor glycoprotein solution (2 mg asialo-a,-acid glycoprotein/acceptor sequence: Gal-ß1,4-Glc NAc-oligosaccharide glycoprotein, 1 mg