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Ascites Tumor Mitochondrial Hexokinase II

EFFECT OF BINDING ON KINETIC PROPERTIES

From the ¹ From the Institute for Cancer Research, Philadelphia, Pennsylvania 19111

Initial rate and product inhibition studies of purified hexokinase II of ELD ascites tumor cells were made with the enzyme both free in solution and in complex with mitochondrial particles. In both forms the enzyme exhibits the random sequence of substrate addition that precedes the rate-limiting step. Inhibition patterns with AMP and ADP are similar in the two forms. Anhydroglucitol-6-P, which was a noncompetitive inhibitor with glucose, was competitive with respect to ATP with the soluble form of the enzyme only. When the enzyme was bound to mitochondria, the inhibition persisted at saturating ATP, suggesting that E·ADP is present in the steady state reaction with the bound enzyme form and that a dead-end complex is formed with anhydroglucitol-6-P. That such a condition could occur with the uncomplexed form of the enzyme was shown with a "slow" substrate, inosine triphosphate, in which anhydroglucitol-6-P was noncompetitive with respect to ITP. Detailed comparison indicates that the soluble enzyme is more sensitive to product inhibition at low ATP concentration and less sensitive at high ATP. The apparent affinity of all inhibitors and of ATP is decreased by the interaction of hexokinase II with glucose.

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				T. Doenst, Q. Han, G. W. Goodwin, P. H. Guthrie, and H. Taegtmeyer Insulin does not change the intracellular distribution of hexokinase in rat heart Am J Physiol Endocrinol Metab, October 1, 1998; 275(4): E558 - E567. [Abstract] [Full Text] [PDF]