Involved in the metabolism of galactose. Catalyzes the conversion of UDP-galactose (UDP-Gal) to UDP-glucose (UDP-Glc) through a mechanism involving the transient reduction of NAD. By controlling the internal galactose concentration, it may be linked to the biosynthesis of lipopolysaccharide surface molecules, which are important for the pathogenesis of H.influenzae. UDP-alpha-D-glucose = UDP-alpha-D-galactose Carbohydrate metabolism; galactose metabolism. Homodimer. Belongs to the NAD(P)-dependent epimerase/dehydratase family.