Vanadium(V) complexes in enzyme systems: aqueous chemistry, inhibition and molecular modeling in inhibitor design

Vanadate in aqueous solution is known to influence a number of enzyme-catalyzed reactions. Such effects are well known to carry over to living systems where numerous responses to the influence of vanadium have been well-documented; perhaps the most studied being the insulin-mimetic effect. Studies of the aqueous chemistry of vanadate provide an insight into the mechanisms by which vanadate affects enzyme systems and suggests methods for the elucidation of specific types of responses. Studies of the corresponding enzymes provide complementary information that suggests model vanadate systems be studied and provides clues as to functional groups that might be utilized in the development of selective enzyme inhibition. The insulin-mimetic effect is thought by many workers to originate in the effectiveness of vanadium as an inhibitor of protein tyrosine phosphatase (PTPase) activity. One, or more PTPases regulate the phosphotyrosine levels of the insulin receptor kinase domain. Appropriate ligands allow modification of the reactivity and function of vanadate. For instance, although the complex, ((CH(3))(2)NO)(2)V(O)OH, is not quite as good an inhibitor of PTPase activity as is vanadate, it is much more effective in cell cultures for increasing glucose transport and glycogen synthesis. Studies of the chemistry of this complex provide an explanation of the efficacy of this compound as a PTPase inhibitor that is supported by computer modeling studies. Computer calculations using X-ray data of known PTPases as a basis for homology modeling then suggests functionality that needs to be addressed in developing selective PTPase inhibitors.