As the recently identified fifth isoform of hexokinase, HKDC1 catalyzes the rate-limiting and first obligatory step of glucose metabolism, which is the ATP-dependent phosphorylation of glucose to G6P. Though its particular biological function remains unclear, HKDC1 has been suggested to play a more major role in glucose metabolism during pregnancy, as the mother would need to provide enough energy for both herself and the fetus. HKDC1 is ubiquitously expressed, with the highest levels of expression in pharynx, thymus, colon, esophagus, and eye tissue.