Competitive inhibition of liver glucokinase by its regulatory protein

Eur J Biochem. 1991 Sep 1;200(2):545-51. doi: 10.1111/j.1432-1033.1991.tb16217.x.


The regulatory protein of rat liver glucokinase (hexokinase IV or D) behaved as a fully competitive inhibitor of this enzyme when glucose was the variable substrate, i.e. it increased the half-saturating concentration of glucose as a linear function of its concentration without affecting V (velocity at infinite concentration of substrate). The inhibition by the regulatory protein and that by palmitoyl-CoA were synergistic with that by N-acetyl-glucosamine, indicating that the two former inhibitors bind to a site distinct from the catalytic site. In contrast, the effects of the regulatory protein and palmitoyl-CoA were competitive with each other, indicating that these two inhibitors bind to the same site. The regulatory protein exerted a non-competitive inhibition with respect to Mg-ATP at concentrations of this nucleotide less than 0.5 mM. At higher concentrations, the latter antagonized the inhibition by the regulatory protein partly by decreasing the apparent affinity for fructose 6-phosphate. The following anions inhibited glucokinase non-competitively with respect to glucose: Pi, sulfate, I-, Br-, No3-, Cl-, F- and acetate. Pi and sulfate, at concentrations in the millimolar range, decreased the inhibition by the regulatory protein by competing with fructose 6-phosphate. Monovalent anions also antagonized the inhibition by the regulatory protein with the following order of potency: I- greater than Br- greater than NO3- greater than Cl- greater than F- greater than acetate and their effect was non-competitive with respect to fructose 6-phosphate. Glucokinase from Buffo marinus and pig liver were, like the rat liver enzyme, inhibited by the regulatory protein, as well as by palmitoyl-CoA at micromolar concentrations. In contrast, neither compound inhibited hexokinases from rat brain, beef heart or yeast, or the low-Km specific glucokinase from Bacillus stearothermophilus.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acetates / pharmacology
  • Acetic Acid
  • Adenosine Triphosphate / metabolism
  • Animals
  • Binding, Competitive
  • Chromatography, Affinity
  • Glucokinase / antagonists & inhibitors*
  • Glucokinase / isolation & purification
  • Glucokinase / metabolism
  • Hexokinase / antagonists & inhibitors
  • Hydrogen-Ion Concentration
  • Kinetics
  • Liver / enzymology*
  • Palmitoyl Coenzyme A / pharmacology
  • Potassium Chloride / pharmacology
  • Rats
  • Sodium Chloride / pharmacology


  • Acetates
  • Palmitoyl Coenzyme A
  • Sodium Chloride
  • Potassium Chloride
  • Adenosine Triphosphate
  • Hexokinase
  • Glucokinase
  • Acetic Acid