The lactose analog GalNAcβ1→4Glc is present in bovine colostrum

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Abstract
We have isolated from bovine colostrum the lactose analog GalNAcβ1→4Glc. The enzymatic basis for its occurrence was studied by assaying the activities of GlcNAcβ-R β4-N-acetylgalactosaminyltransferase (β4-GalNAcT) and GlcNAcβ-R β4-galactosyltransferase (β4-GalT) in primary milk and several lactating bovine mammary gland fractions. As the β4-GalNAcT, which appears to be tightly membrane bound, is induced by the milk protein α-lactalbumin (α-LA) to act on Glc, it is concluded that β4-GalNAcT is responsible for the synthesis of GalNAcβ1→4Glc in the gland. The comparatively low level (15–20 mg/l) at which this disaccharide is produced may be due to the relatively poor interaction of β4-GalNAcT with α-LA as well as to the fact that α-LA does not inhibit the action of the enzyme on N-acetylglucosaminides.