Plays an important role in galactose metabolism. alpha-D-galactose 1-phosphate + UDP-alpha-D-glucose = alpha-D-glucose 1-phosphate + UDP-alpha-D-galactose Binds 2 zinc ions per subunit. Carbohydrate metabolism; galactose metabolism. Homodimer. Belongs to the galactose-1-phosphate uridylyltransferase type 1 family.