ALPHA-1,3-FUCOSYLATION OF BRANCHED BLOOD-GROUP I-TYPE OLIGO-(N-ACETYLLACTOSAMINO)GLYCANS BY HUMAN-MILK TRANSFERASES IS RESTRICTED TO DISTALN-ACETYLLACTOSAMINE UNITS - THE RESULTING ISOMERS ARE SEPARATED BY WGA-AGAROSE CHROMATOGRAPHY

A partially purified preparation of alpha 1,3-fucosyltransferase(s) fr om human milk was used to [C-14]fucosylate oligosaccharides containing Gal beta 1-4GlcNAc units. Substitution of N-acetyllactosamine at posi tion 3' with a beta-linked N-acetyl-glucosamine enhanced the reactivit y of the acceptor, whereas similar substitution at position 6' was inh ibitory. Thus, the trisaccharide GlcNAc beta 1-6Gal beta 1-4GlcNAc (5) , the branched tetrasaccharide GlcNAc beta 1-3(GlcNAc beta 1-6)Gal bet a 1-4GlcNAc (11) and the triply branched decasaccharide GlcNAc beta 1- 3(GlcNAc beta 1-6)Gal beta 1-4GlcNAc beta 1-3[GlcNAc beta 1-3(GlcNAc b eta 1-6)Gal beta 1-4GlcNAc beta 1-6]Gal beta 1-4GlcNAc (26) gave remar kably poor yields of alpha 1,3-fucosylated products in comparison to G lcNAc beta 1-3Gal beta 1-4GlcNAc (3). pl,4-Galactosyl derivatives of 5 and 11, however, gave good yields of alpha 1,3-fucosylated products, but the fucosylation was restricted to the distal N-acetyllactosamine units of Gal beta 1-4GlcNAc beta 1-6Cal beta 1-4GlcNAc (16), Gal beta 1-4GlcNAc beta 1-3(Gal beta 1-4GlcNAc beta 1-6)Gal beta 1-4GlcNAc (18) and also in Gal alpha 1-3Gal beta 1-4GlcNAc beta 1-3(Gal alpha 1-3Gal beta 1-4GlcNAc beta 1-6)Gal beta 1-4GlcNAc (22). Immobilized wheat ge rm agglutinin (WGA), possessing high affinity for 16 [1], revealed no affinity for the fucosylated derivative Gal beta 1-4(Fuc alpha 1-3)Glc NAc beta 1-6Gal beta 1-4GlcNAc (17). The isomeric heptasaccharides Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3(Gal beta 1-4GlcNAc beta 1-6)Ga l beta 1-4GlcNAc (19) and Gal beta 1-4GlcNAc beta 1-3[Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-6]Gal beta 1-4GlcNAc (20) were readily separa ted from each other on WGA-agarose, and so were the isomeric nonasacch arides Gal alpha 1-3Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3(Gal alp ha 1-3Gal beta 1-4GlcNAc beta 1-6)Gal beta 1-4GlcNAc (23) and Gal alph a 1-3Gal beta 1-4GlcNAc beta 1-3[Gal alpha 1-3Gal beta 1-4(Fuc alpha 1 -3)GlcNAc beta 1-6]Gal beta 1-4GlcNAc (24).