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 Km 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-GM1 :
sialyltransferase, but had an increased activity of asialo-GM3 :
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.