Galactosyltransferase-dependent sialylation of complex and endo-N-acetylglucosaminidase H-treated core N-glycans in vitro.

Purified beta-N-acetylglucosaminide beta(1-4)galactosyltransferase and partially purified beta-galactoside alpha(2-6)-sialyltransferase were used to elongate and terminate glycan chains of agalacto-ovalbumin and endo-beta-N-acetylglucosaminidase H-treated yeast invertase in vitro. In the presence of both transferases, 0.1 mol sialic acid was incorporated per mol agalacto-ovalbumin within 24 h. Evidence is presented to show that purification of the galactosylated intermediate increases the efficiency of sialylation. Incorporation of sialic acid into endo-beta-N-acetylglucosaminidase H-treated oligomannose glycoproteins may be useful for in vivo stabilization of these glycoproteins by preventing uptake in liver or reticuloendothelial cells.