An enzymatic basis for Lewis blood types in man.

Milk from women with blood type Le(a+) or Le(b+) contains a specific fucosyltransferase not found in the milk of women with blood type Le(a- b-). The enzyme, a guanosine diphosphate L-fucose: N-acetyl-beta-D-glucosaminylsaccharide alpha-4-L-fucosyltransferase is apparently required for the synthesis of the structural determinants of Le(a) and Le(b) specificity, both of which contain fucose in an alpha-1,4 linkage to N-acetylglucosamine. The same enzyme is also involved in the synthesis of milk oligosaccharides, as two oligosaccharides which contain this linkage are absent from the milk of women with Le(a- b-) blood type.