Reassessment of the acceptor specificity and general properties of the Lewis blood-group gene associated alpha-3/4-fucosyltransferase purified from human milk.

The acceptor specificity and general properties of a Lewis blood-group gene associated alpha-3/4-L-fucosyltransferase isolated from human milk have been examined at the penultimate purification stage involving affinity chromatography on GDP-hexanolamine Sepharose, and after a subsequent gel filtration step on Sephacryl S-200. Both preparations transferred fucose to the O-4 position of N-acetylglucosamine in Type 1 (Gal beta 1-3GlcNAc-R) acceptors and the O-3 position of glucose in lactose-based (Gal beta 1-4Glc) oligosaccharides, and both used Type 1 sialylated compounds when the terminal N-acetylneuraminic acid was present in alpha-2,3 linkage. The striking difference between the two preparations was in their reactivity with Type 2 (Gal beta 1-4GlcNAc-R) chains; after Sephacryl S-200 chromatography the apparent KM values for the alpha-3/4- preparation with unsubstituted low-molecular-weight Type 2 oligosaccharides were considerably increased. Substitution of the terminal galactose with sialic acid in alpha-2,3 linkage decreased the KM values for low-molecular-weight oligosaccharides but no detectable incorporation of fucose was observed into N-acetyllactosamine end-groups of glycoproteins with N-linked oligosaccharide chains, irrespective of the presence of sialic acid in the terminal sequences.