The Leloir pathway is a metabolic pathway for the catabolism of <small>D</small>-galactose. It is named after Luis Federico Leloir, who first described it.
In the first step, galactose mutarotase facilitates the conversion of ò-<small>D</small>-galactose to ñ-<small>D</small>-galactose since this is the active form in the pathway. Next, ñ-<small>D</small>-galactose is phosphorylated by galactokinase to galactose 1-phosphate. In the third step, <small>D</small>-galactose-1-phosphate uridylyltransferase converts galactose 1-phosphate to UDP-galactose using UDP-glucose as the uridine diphosphate source. Finally, UDP-galactose 4-epimerase recycles the UDP-galactose to UDP-glucose for the transferase reaction. Additionally, phosphoglucomutase converts the <small>D</small>-glucose 1-phosphate to <small>D</small>-glucose 6-phosphate.