Sialyl- and galactosyltransferases in the human chorionic gonadotropin-treated immature rat ovary

General properties of glycoprotein sialyl- and galactosyltransferases in control and hCG-primed immature rat ovary were studied by using asialo and agalacto derivatives of fetuin, alpha 1-acid glycoprotein, and purified O-glycosidically linked fetuin glycopeptide as exogenous substrates. Incorporation of the labeled sugars into the derivatives was determined by electrophoresis and precipitation with phosphotugnstic acid and with a rabbit anti-fetuin gamma-globulin fraction. Both enzyme activities were associated with partiulcate fractions, were enhanced by 0.3% Triton X-100, had pH optima between 6.3-6.6, and exhibited apparent Km values of 0.04-0.08 mM for the sugar nucleotides and 0.3-0.6 mM for the asialo- and asialoagalactofetuin derivatives. The galactosyltransferase required exogenous Mn+2 for activity. The specific activities of galactosyltransferase were similar in the control and hCG-primed ovaries, while the specific activity of sialytransferase in the hCG-primed ovaries was consistently twice that in the control.