SHORT-TERM CONTROL OF GLUCOKINASE ACTIVITY - ROLE OF A REGULATORY PROTEIN

Glucokinase is one of the four hexokinases present in mammalian tissue s. It is expressed in two cell types that have to respond to changes i n the blood glucose concentration, the liver parenchymal cell and the P-cells of pancreatic islets. The former are responsible for the metab olism and storage of an important part of the ingested glucose, wherea s the latter secrete insulin in response to an increase in the blood g lucose level. One major characteristic of glucokinase is that it has a relatively low affinity for glucose and displays positive cooperativi ty for this substrate, despite the fact that it is a monomeric enzyme. Furthermore, unlike other hexokinases, it is not inhibited by micromo lar (physiological) concentrations of glucose 6-phosphate but by a reg ulatory protein that transduces the effect of fructose 6-phosphate and of fructose 1-phosphate. The purpose of this review is to describe th ese aspects of the regulation of glucokinase.