Glucokinase is the name given to a special liver form of the enzyme hexokinase. Like hexokinase, glucokinase catalyzes the ATP-dependent phosphorylation of glucose to form glucose-6-phosphate (G6P) and ADP. This is the first step of glycolysis. The enzyme will act on a variety of 6-carbon sugars, producing moieties phosphorylated at position six. Glucokinase, however, has a higher KM for sugar substrate compared to hexokinase (10 mM vs. 1 mM). This difference is very important for the liver, which is a major source of glucose from gluconeogenesis. The higher KM for glucokinase means that less glucose will be phosphorylated, allowing more glucose to be exported to the bloodstream, where it can be delivered to other tissues that do not make their own glucose. This may be particularly important during exercise, when muscle cells rapidly exhaust their endogenous supply of glucose. This is an essential part of the Cori cycle.

Glucokinase is not involved in the process of gluconeogenesis. Instead, the enzyme glucose-6-phosphatase catalyzes the hydrolysis of G6P to glucose and Pi, bypassing the large of the glucokinase-catalyzed reaction.

Next step of glycolysis; Enzymes of glycolysis; Glycolysis overview

INTERNET LINK: for RasMol Structure (slow)