UDP-glucose 4-epimerase, a member of the NAD(P)-dependent epimerase (dehydratase) family, is also known as galactowaldenase (GALE), UDP-N-acetylgalactosamine 4-epimerase (UDP-GalNAc 4-epimerase) and UDP-N-acetylglucosamine 4-epimerase (UDP-GlcNAc 4-epimerase),which is a homodimeric epimerase found in bacterial, fungal, plant, and mammalian cells. GALE can catalyze two distinct but analogous reactions: the reversible epimerization of UDP-glucose to UDP-galactose and the reversible epimerization of UDP-N-acetylglucosamine to UDP-N-acetylgalactosamine. The reaction with UDP-Gal plays a critical role in the Leloir pathway of galactose catabolism in which galactose is converted to the glycolytic intermediate glucose 6-phosphate. It contributes to the catabolism of dietary galactose and enables the endogenous biosynthesis of both UDP-Gal and GALE (UDP-GalNAc) when exogenous sources are limited. Both UDP-sugar interconversions are important in the synthesis of glycoproteins and glycolipids.