Structure and Function of Enzymes of the Leloir Pathway for Galactose Metabolism

In most organisms, the conversion of β-d-galactose to the more metabolically useful glucose 1-phosphate is accomplished by the action of four enzymes that constitute the Leloir pathway (Scheme 1). In the first step of this pathway, β-d-galactose is epimerized to α-d-galactose by galactose mutarotase. The next step involves the ATP-dependent phosphorylation of α-d-galactose by galactokinase to yield galactose 1-phosphate. As indicated in Scheme 1, the third enzyme in the pathway, galactose-1-phosphate uridylyltransferase, catalyzes the transfer of a UMP group from UDP-glucose to galactose 1-phosphate, thereby generating glucose 1-phosphate and UDP-galactose.