Vanadate tetramer as the inhibiting species in enzyme reactions in vitro and in vivo

Article abstract of DOI:10.1021/ja00157a063

Tetrameric vanadate polyanion inhibits 6-phosphogluconate dehydrogenases from human, mammalian, yeast, and bacterial sources. The inhibition by a vanadate mixture containing monomer, dimer, and tetramer was determined by measuring the rates of 6-phosphogluconate oxidation and NADP (or NAD) reduction catalyzed by 6-phosphogluconate dehydrogenase. The inhibition by vanadate is competitive with respect to 6-phosphogluconate and mixed or noncompetitive with respect to NADP or NAD. ⁵¹V NMR spectroscopy was used to direcly correlate the inhibition of vanadate solutions to the vanadate tetramer. The measured inhibition constants with respect to 6-phosphogluconate for the tetramer are 0.078 mM for the human erythrocyte enzyme, 0.063 mM for the sheep liver enzyme, 0.013 mM for the yeast enzyme, and 0.24 mM for the Leuconostoc mesenteroides. The observed inhibition of 6-phosphogluconate dehydrogenase by vanadate tetramer is the first enzymatic activity observed of this polyanion. Our observations suggest the vanadate tetramer will be a potent inhibitor to other organic phosphate converting enzymes and preliminary results confirm this expectation. The vanadate tetramer may be an important species when considering the mechanism by which vanadium acts in biological systems in vitro and in vivo.