Galactosyltransferase Acceptor Specificity of the Lactose Synthetase A Protein

Abstract

Abstract The galactosyl acceptor specificity of the highly purified A protein (galactosyltransferase) isolated from bovine milk was examined in the absence and presence of α-lactalbumin. α-Lactalbumin inhibits the transfer of galactose to N-acetylglucosamine but does not appreciably inhibit the transfer to oligomers of N-acetylglucosamine and other β-1,4 linked glycosides such as cellobiose, cellobiulose (glucosyl-β-1,4-fructose), β-d-methylglucose, glucosyl-β-1,4-mannose, indoxyl-β-d-glucose, and ovalbumin. α-Glycosides are poor substrates in the presence of α-lactalbumin but are not substrates in its absence. The biosynthesis of lactose and the formulation of the Gal-β-1,4-GlcNAc linkage in the carbohydrate side chain of glycoproteins are compatible and are carried out by the same galactosyltransferase.