Comparative Study of the Levels of Sialyltransferases Responsible for the Formation of Sugar Chains in Glycoproteins and Gangliosides in Rat Liver and Hepatomas

摘要

Sialyltransferases responsible for the formation of sugar chains in glycoproteins were studied in rat hepatoma in comparison with rat liver. Hepatoma induced by feeding Wistar rats with 3′‐ methyl‐4‐dimethyIaminoazobenzene (MeDAB) was more active than Wistar liver in sialylating asialo‐orosomucoid, and this was due to an increased activity of GaI(β1→4)GlcNAc (α→6) sialyltransferase, the major sialyltransferase in these tissues, Gal(β1→3,4)GlcNAc (α→3) sialyltransferase and the sialyltransferases acting on asialo‐bovine submaxillary mucin were, however, decreased in the hepatoma. A similar pattern of sialyltransferase alterations was observed in regenerating liver and other tumors such as AH‐109A hepatoma and Sato lung cancer, both of which had been inoculated into Donryu rats. In contrast to these sialyltransferases, the activities of the sialyltransferases responsible for the formation of gangliosides were markedly different even between Wistar and Donryu livers. When compared with Wistar liver, MeDAB induced hepatoma was higher in lactosylceramide‐ and lower in GM³‐sialyltransferase activity, but these two activities were both lower in AH‐109A compared with Donryu liver.