UDP-Galactose is especially relevant in glycolysis. It is derived from galactose 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.