Effect of inorganic phosphate on the reverse reaction of bovine brain hexokinase

Abstract

Kinetic studies were used to investigate the mode of brain hexokinase regulation by G-6-P, ADP and Pi. A model for regulation of brain hexokinase by G-6-P and Pi had been proposed from initial-rate studies and binding experiments. Pi is an activator of the brain hexokinase reaction when the reaction is studied in the nonphysiological direction. The back-reaction substrates and Pi can bind the enzyme simultaneously, and Pi may bind to an allosteric site on the enzyme. These findings are in marked contrast to results obtained in the absence of ADP which convincingly demonstrate that G-6-P and Pi are mutually exclusive binding ligands for brain hexokinase. The kinetic data can be reconciled with the model for hexokinase regulation within the context of the well-established kinetic mechanism for brain hexokinase.