The penta-coordinated vanadium formed on binding of ADP-vanadate-Mg(II) to CF₁-ATPase functions as a transition-state inhibitor

The structure of vanadate, a phosphate analogue which functions in the presence of tightly bound ADP and divalent cations as a transition state inhibitor of CF₁-ATPase, was investigated by X-ray absorption spectroscopy. There was a decrease in the intensity of the pre-edge transition and a change in the shape and energy of the K-edge upon binding of ADP-vanadate-Mg(II) to CF₁. The changes were due to alterations in the structure of vanadium from tetrahedral to five-coordinated trigonal bipyramidal geometry. Simulation of the edge shape and energies and EXAFS analysis confirmed the presence of pentacoordinated vanadium bound to the enzyme. This structure was analogous to the proposed transition state of the phosphate during the synthesis and the hydrolysis of ATP by CF₁.