Studies on sialyltransferases of fetal calf liver

Abstract

Asialofetuin sialyltransferase from Triton X-100 extracts of fetal calf liver resolved by phosphocellulose column chromatography into two fractions, designated A and B in order of elution. Survey of the isomeric nature of sialyllactose formed and also of efficiencies of various substrates, which include asialofetuin, β-eliminated asialofetuin, asialoorosomucoid and bovine and porcine submaxillary mucins, has made it clear that fraction A contains Galβ1→4GlcNAcα2→6 sialyltransferase (associated with the synthesis of N-glycosidicaly linked sugar chains) while fraction B contains Galβ 1→3 GalNAc α2→3 sialyltransferase (associated with the synthesis of O-glycosidically linked sugar chains). In addition, fraction A appears to contain a small amount of another sialyltransferase that transfers sialic acidα 2→3 g, lycosidically to N-glycosidically linked sugar chains, but its separation from the majorα 2→6 enzyme has yet been unsuccessful. The chromatographic conditions shown above have been utilized to demonstrate (i) that the major sialyltransferase of the rat liver and human placenta is identical to the above-described A and B, respectively, and (ii) that even primary rat hepatoma induced by 3'-methyl-4-dimethylaminoazobenzene contains no Galβ1→3 Ga1NAc α 2→3 sialyltransferase.