Galactokinase (GALK; EC 2.7.1.6) catalyzes the conversion of α-D-galactose to galactose 1-phosphate, the second step in the pathway of the conversion of β-D-galactose, to the more metabolically useful glucose 1-phosphate (Leloir pathway). Defects in the human enzyme can result in the diseased state referred to as galactosemia. Additionally, galactokinase-like molecules have been shown to act as sensors for the intracellular concentration of galactose and, under suitable conditions, to function as transcriptional regulators.