Im. Van Den Nieuwenhof et al., The lactose analog GalNAc beta 1 -> 4Glc is present in bovine colostrum - Enzymatic basis for its occurrence, FEBS LETTER, 459(3), 1999, pp. 377-380
We have isolated from bovine colostrum the lactose analog GalNAc beta 1-->4
Glc. The enzymatic basis for its occurrence was studied by assaying the act
ivities of GlcNAc beta-R beta 4-N-acetylgalactosaminyltransferase (beta 4-G
alNAcT) and GlcNAc beta-R beta 4-galactosyltransferase (beta 4-GalT) in pri
mary milk and several lactating bovine mammary gland fractions. As the beta
4-GalNAcT, which appears to be tightly membrane bound, is induced by the m
ilk protein alpha-lactalbumin (alpha-LA) to act on Glc, it is concluded tha
t beta 4-GalNAcT is responsible for the synthesis of GalNAc beta 1-->4Glc i
n the gland. The comparatively low level (15-20 mg/l) at which this disacch
aride is produced may be due to the relatively poor interaction of beta 4-G
alNAcT with alpha-LA as well as to the fact that alpha-LA does not inhibit
the action of the enzyme on N-acetylglucosaminides. (C) 1999 Federation of
European Biochemical Societies.