Sialyltransferase in fetal tissues: Incorporation of sialic acid into endogenous and exogenous glycoprotein acceptors

Abstract

The properties of exogenous sialyltransferase activity in fetal mouse liver were compared with the endogenous enzyme activity. Nonionic detergents such as Tergitol inhibited endogenous activity but released the enzyme from the 30,000 g particulate fraction and allowed it to react with the exogenous glycoprotein acceptors, partially desialylated α-fetoprotein and calf fetuin. Zinc ions partially transferred the enzyme activity from the particulate fraction to the supernatant, while incubation at 45 °C preferentially inhibited endogenous enzyme activity. α-Fetoprotein, sialylated by the endogenous enzyme preparation, was determined to be 7% of the total incorporation of radioactivity by immunoprecipitation with mouse anti-α-fetoprotein and subsequent sodium dodecyl sulfate-polyacrylamide-gel electrophoresis. Sialyltransferase activity in fetal liver, yolk sac, placenta and embryo (minus liver) was measured during development. Exogenous enzyme activity of liver in early development (day 13.5) was twice as high as that in yolk-sac tissues that synthesize α-fetoprotein. Furthermore, enzyme activity increased 12-fold in fetal liver and 4-fold in yolk sac by day 18.5 of development. Activity in placenta increased 2.9-fold and then decreased, while embryo (minus liver) showed no increase. Endogenous enzyme activity increased temporally in these tissues, but the increase was less than that measured by using exogenous acceptors.