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 Mg(2+)-dependent mechanism. After incubation with an elevated [glucose] or with fructose, glucokinase, but not its regulatory protein, translocates from the Mg(2+)-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.

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