Hexokinase Inhibition after the Addition of Glucose to Ehrlich-Lettré Ascites Tumor Cells under Aerobiosis

Some kinetic properties of the soluble and the mitochondrially bound hexokinases of Ehrlich-Lettre ascites tumor cells were examined. Both enzyme forms were essentially kinetically identical, and both were found to be exceedingly sensitive to inhibition by glucose-6-phosphate. Ki values in the absence of Pi at 1 and at 2 mm ATP were 0.019 and 0.035 mm glucose-6-P, respectively, for the bound enzyme. In agreement with the results of others, added Pi (3 mm) increased the Ki values to 0.034, 0.045, and 0.060 mm glucose-6-P at 1, 2.5, and 5 mm ATP, respectively. Glucose-6-P was a mixed inhibitor with respect to ATP. A 90 to 95% inhibition of hexokinase was found when the ratio of ATP to glucose-6-P approached 3 at 1 mm ATP and 3 mm Pi. A comparison of these kinetic results with the ATP and glucose-6-P levels observed in intact Ehrlich-Lettre ascites cells incubated in air indicated that the marked inhibition of glucose uptake which begins 1 to 2 min after glucose addition may be explained by the hexokinase inhibition expected because of the accumulated glucose-6-P. It does not appear necessary to postulate other hexokinase control mechanisms in these cells.