The Relationship between the (β1-3) N-Acetylglucosaminyltransferase and the Presence of Oligosaccharides Containing Lacto-N-triose II Structure in Bovine and Human Milk

Abstract

We measured UDP-GlcNAc:Gal (β1-4) Glc (or GlcNAc) (β1-3) N-acetyl-glucosaminyltransferase activities in bovine (Holstein and Jersey cow) and human colostrums, and found in human colostrums sufficient activity to study the enzyme properites while not in bovine colostrums. The properties (requirements, pH optimum, acceptor specificity and Km values for lactose and N-acetyllactosamine) of the enzyme from human colostrum were very similar to those from human serum and urine. The reaction product was hydrolyzed by β-N-acetylhexosaminidase, indicating that the N-acetylglucosaminyl residue was β-linked to lactose. Methylation and hydrolysis of the reaction product from lactose [₃H] labeled at the terminal galactose yielded 2, 4, 6-tri-O-methyl [₃H] galactose. Thus the structure of the product was demonstrated to be GlcNAc (β1-3) Gal (β1-4) Glc (lacto-N-triose II). On the other hand, bovine sera contained N-acetylglucosaminyltransferase catalyzing the transfer of N-acetylglucosamine from UDP-GlcNAc to lactose. The enzyme activities were approximately 1/6-1/4 of that contained in human serum. The presence of (β1-3) N-acetylglcosaminyltransferase in human colostrum and its absence in bovine colostrums, apparently corresponds with the presence and absence of oligosaccharides containing lacto-N-triose II structure in colostrum.