Mutarotase that catalyzes the interconversion of beta-D-galactose and alpha-D-galactose during galactose metabolism. Beta-D-galactose is metabolized in the liver into glucose 1-phosphate, the primary metabolic fuel, by the action of four enzymes that constitute the Leloir pathway: GALM, GALK1 (galactokinase), GALT (galactose-1-phosphate uridylyltransferase) and GALE (UDP-galactose-4'-epimerase). Involved in the maintenance of the equilibrium between the beta- and alpha-anomers of galactose, therefore ensuring a sufficient supply of the alpha-anomer for GALK1. Also active on D-glucose although shows a preference for galactose over glucose. alpha-D-galactose = beta-D-galactose alpha-D-glucose = beta-D-glucose Carbohydrate metabolism; hexose metabolism. Carbohydrate metabolism; galactose metabolism. Monomer. Belongs to the aldose epimerase family.