Biosynthesis of Fucosyllactose and Other Oligosaccharides Found in Milk.

The carbohydrate fraction of human milk includes a number of chemically defined oligosaccharides which contain the 6-deoxyhexose, L-fucose (2, 3). The present report describes a particulate enzyme from lactating canine mammary tissue’ which catalyzes the synthesis of fucosyllactose,2 the simplest member of this group, by transfer of L-fucose from guanosine diphosphate L-fucose to lactose. If fucosyllactose were formed by the preceding reaction in viva, the lactose moiety of the trisaccharide should arise from free lactose and, as a consequence, resemble it in 14C distribution after administration of a labeled precursor. This metabolic relationship was investigated in lactating dogs by modifying the technique used by Wood, Siu, and Schambye (5) in their extensive investigations of lactose synthesis by the bovine mammary gland. Glycerol-% was injected into the artery supplying the mammary gland, and the amount and distribution of radioactivity were determined in the oligosaccharides subsequently isolated from the milk. In addition to lactose and fucosyllactose, sialyllactose and a higher oligosaccharide fraction were isolated, and the specific activities of their component sugars were determined. The results indicate that n-glucose is the initial acceptor to which other sugars are sequentially transferred in the biosynthesis of fucosyllactose as well as other oligosaccharides found in milk.