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 modu lated by binding to a regulatory protein. This study shows that, in he patocytes 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 [glucos e] or with fructose, glucokinase, but not its regulatory protein, tran slocates from the Mg2+-dependent binding site. It is suggested that th e regulatory protein acts as a receptor for anchoring glucokinase to t he hepatocyte matrix and inhibiting its activity in metabolically quie scent conditions.