The lactose analog GalNAcbeta1-->4Glc is present in bovine colostrum. Enzymatic basis for its occurrence.
We have isolated from bovine colostrum the lactose analog GalNAcbeta1-->4Glc. The enzymatic basis for its occurrence was studied by assaying the activities of GlcNAcbeta-R beta4-N-acetylgalactosaminyltransferase (beta4-GalNAcT) and GlcNAcbeta-R beta4-galactosyltransferase (beta4-GalT) in primary milk and several lactating bovine mammary gland fractions. As the beta4-GalNAcT, which appears to be tightly membrane bound, is induced by the milk protein alpha-lactalbumin (alpha-LA) to act on Glc, it is concluded that beta4-GalNAcT is responsible for the synthesis of GalNAcbeta1-->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 beta4-GalNAcT with alpha-LA as well as to the fact that alpha-LA does not inhibit the action of the enzyme on N-acetylglucosaminides.
Van den Nieuwenhof
I M
IM
Department of Medical Chemistry, Faculty of Medicine, Vrije Universiteit, Van der Boechorststraat 7, 1081 BT, Amsterdam, The Netherlands. im.van_den_nieuwenhof.medchem@med.vu.nl
Schiphorst
W E
WE
Van den Eijnden
D H
DH
D000818:Animals; D001940:Breast / Q000201:enzymology; D002417:Cattle; D003126:Colostrum / Q000737:chemistry* / Q000201:enzymology; D004187:Disaccharides / Q000032:analysis* / Q000737:chemistry; D066298:In Vitro Techniques; D007785:Lactose / Q000031:analogs & derivatives*; D008892:Milk / Q000201:enzymology; D017350:N-Acetylgalactosaminyltransferases / Q000378:metabolism; D009237:N-Acetyllactosamine Synthase / Q000378:metabolism; D009844:Oligosaccharides / Q000302:isolation & purification / Q000378:metabolism; D000097763:Polypeptide N-acetylgalactosaminyltransferase
D004187:Disaccharides; D007785:Lactose; D017350:N-Acetylgalactosaminyltransferases; D009237:N-Acetyllactosamine Synthase; D009844:Oligosaccharides; D000097763:Polypeptide N-acetylgalactosaminyltransferase; C042746:N-acetylgalactosaminyl-(1-4)-glucose