Uridine diphosphate galactose (UDP-galactose) is an intermediate in the production of polysaccharides. It is important in nucleotide sugars metabolism, and is the substrate for the transferase B4GALT5.
Uridine diphosphate (UDP)-galactose is relevant in glycolysis. UDP-galactose is the activated form of Gal, a crucial monosaccharide building block for human milk oligosaccharide (HMO). The activated form of galactose (Gal) serves as a donor molecule involved in catalyzing the conversion of UDP-galactose to UDP-glucose. The conversion is a rate-limiting step essential to the pace of UDP-glucose production that determines the completion of glycosylation reactions.
To further explain, UDP-galactose is derived from a galactose molecule which is an epimer of glucose, and via the Leloir pathway, it is used be used as a precursor for the metabolism of glucose into pyruvate. When lactose is hydrolyzed, D-Galactose enters the liver via the bloodstream. There, galactokinase phosphorylates it to galactose-1-phosphate using ATP. This compound then engages in a "ping-pong" reaction with UDP-glucose, catalyzed by uridylyltransferase, yielding glucose-1-phosphate and UDP-galactose. This glucose-1-phosphate feeds into glycolysis, while UDP-galactose undergoes epimerization to regenerate UDP-glucose.