Glycosylation of kappa-casein. I. Localization and characterization of sialyltransferase in bovine mammary gland.
A sialyltransferase (CMP-N-acetylneuraminate:D-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1) which attaches N-acetylneuraminic acid to the terminal end of the carbohydrate chain of kappa-casein was found to be concentrated in Golgi apparatus-enriched fractions of bovine mammary gland. Maximum sialyltransferase activity was obtained at pH 5.5 and 37 degrees C in the presence of 1 mM dithiothreitol and Triton X-100. A Km of 0.19 mg asialo-kappa-casein/ml (0.01 mM) was obtained for the sialyltransferase. Native kappa-casein also served as acceptor for N-acetylneuraminic acid transferase of Golgi apparatus-enriched fractions although at a slower rate than did asialo-kappa-casein. The sialyltransferase has a divalent cation requirement for maximum activity which was best satisfied by the presence of 10 mM Mn2+.
D000818:Animals; D002364:Caseins / Q000378:metabolism*; D002413:Cations, Divalent / Q000494:pharmacology; D002417:Cattle; D004229:Dithiothreitol / Q000494:pharmacology; D005260:Female; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008321:Mammary Glands, Animal / Q000201:enzymology*; D011092:Polyethylene Glycols / Q000494:pharmacology; D011247:Pregnancy; D012799:Sialyltransferases / Q000378:metabolism*; D013347:Subcellular Fractions / Q000201:enzymology; D013696:Temperature; D014018:Tissue Distribution; D014166:Transferases / Q000378:metabolism*
D002364:Caseins; D002413:Cations, Divalent; D011092:Polyethylene Glycols; D014166:Transferases; D012799:Sialyltransferases; D004229:Dithiothreitol