Inhibition of hexokinase by multisubstrate analogs.

The compounds P1-(adenosine-5')-P3-(glucose-6) triphosphate (Ap3 glucose) and P1-(adenosine-5')-P4-(glucose-6)tetraphosphate (Ap4 glucose) were synthesized as possible transition-state analogs for hexokinase (ATP: D-hexose 6- phosphotransferase, EC 2.7.1.1). Both compounds were inhibitors of this enzyme, competitive against ATP and apparently uncompetitive against glucose. The inhibition constants for Ap3 glucose and Ap4 glucose were 0.43 mM and 0.37 mM, respectively. These results indicate that the inhibitors do not appreciably bind to hexokinase until the glucose binding site is filled. The sugar portion of the inhibitors therefore does not contribute to binding, and the compounds are acting as ATP analogs, Ap3 glucose and Ap4 glucose are also slow substrates for glucose-6-phosphate dehydrogenase.