Uridine diphosphate-galactose synthesis

Enzymatic synthesis of uridine diphosphate glucose has been observed, but there are no published reports on how the synthesis takes place. However, we do have some indication of how the compound may act as a coenzyme. When incubated with an extract of S. fragilis it is transformed into uridine diphosphate galactose. This would be a biological Walden inversion. Discovery of this reaction has led to the following hypothesis for the mechanism of the conversion of galactose-1-phosphate to glucose-l-phosphate ... 

Wong C-H, Haynle SL, Whitesides GM. Enzyme-catalyzed synthesis of iV-Acetyllactosamine with in situ regeneration of uridine 5 -diphosphate glucose and uridine 5 -diphosphate galactose. J. Org. Chem. 1982 47 5416-5418. 

Galactose 1-phosphate then acquires a uridyl group from uridine diphosphate glucose (UDP-glucose), an intermediate in the synthesis of glycosidic linkages (Section 21.4.2). 

Figure 11.22 Possible pathways for the synthesis of gangliosides. Cer, ceramide Glc, glucose Gal, galactose GalNAc, N-acetylgalactos-amine CMP, cytidine monophosphate NANA, A/-acetylneuraminic add (sialic acid) UDP, uridine diphosphate. Reproduced from Gurr and James (1980) with permission.

L. is the most important carbohydrate in the milk of all mammals. Human milk contains 6-8%, cow s milk 4-5%. L. is a component of a few oligosaccharides, and also occurs in plants, e.g. in fruits and pollen. In L. synthesis in the milk glands of mammals, the galactose residue of uridine diphosphate p-galac-tose is transferred and linked to the OH on C4 of d-glucose, a process catalysed by lactose synthetase,... 

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