Characterization of Glycosyltransferases in the Golgi Complex from Rat Ascites Hepatoma AH-130 Cells: A Comparison with Those from Normal Liver1

Abstract

We isolated the Golgi-rich fraction from rat ascites hepatoma AH-130 cells and rat liver, and compared some properties of glycosyltransferases using various acceptors. The specific activity of sialyltransferase in the hepatoma Golgi fractions was reduced to 19–41% depending upon the acceptor used (asialo-orosomucoid, asialo-fetuin or asialo-mucin), as compared to that of the normal liver Golgi fraction. However, no significant difference between the enzymes from the two sources was observed in pH optimum, requirements for the enzyme activity, and K_m values for the donor substrate (CMP-sialic acid) and various acceptors used. The specific activity and other kinetic parameters of hepatoma galactosyltransferase were not significantly different from those of the liver enzyme, when assayed with N -acetylglucosamine, asialo-agalacto-fetuin and asialomucin as acceptors. Glycosyltransferases in the hepatoma and liver Golgi fractions were then assayed with plasma membranes from both sources as exogenous acceptor. Hepatoma sialyltransferase activity was much lower (1/2 to 1/4) than that of the normal liver. Galactosyltransferase activity, however, was found to be slightly higher in the hepatoma Golgi fraction than in the normal liver. Acceptor plasma membranes which were thus glycosylated in vitro by each Golgi enzyme were separated into protein and lipid fractions, and the latter fraction was further analyzed by thin layer chromatography. The results suggest that the hepatoma Golgi had much lower levels of glycoprotein : sialyltransferase and asialo-GM ₁ : sialyltransferase, but had an increased activity of asialo-GM ₃ : sialyltransferase. It is also suggested that the hepatoma Golgi had a high activity for the formation of di- and tri-glycosylceramides, for which the liver Golgi showed negligible activity.