THE REGULATORY PROTEIN OF GLUCOKINASE BINDS TO THE HEPATOCYTE MATRIX, BUT, UNLIKE GLUCOKINASE, DOES NOT TRANSLOCATE DURING SUBSTRATE STIMULATION

The kinetic properties of hepatic glucokinase (hexokinase IV) are modulated by binding to a regulatory protein. This study shows that, in hepatocytes incubated with 5 mM glucose as sole carbohydrate substrate, both glucokinase and its regulatory protein bind to the cell matrix by a Mg2+-dependent mechanism. After incubation with an elevated [glucose] or with fructose, glucokinase, but not its regulatory protein, translocates from the Mg2+-dependent binding site. It is suggested that the regulatory protein acts as a receptor for anchoring glucokinase to the hepatocyte matrix and inhibiting its activity in metabolically quiescent conditions.