In the short time since 1977, when it was discovered that vanadate is a potent inhibitor of the sodium pump (Na,K-ATPase), vanadium has become a valuable and widely used probe of enzyme function and mechanism. In the V(V) oxidation state, as diamagnetic vanadate, it mimics phosphate and interacts with a large class of phosphatases and phosphotransferases. In the V(IV) oxidation state, as paramagnetic vanadyl, it behaves as a transition metal ion and can replace other such ions in metalloproteins. Because the potentials of V(V) and V(IV) lie within limits tolerated by living systems, vanadium can also participate in many biological electron transfer reactions. The wide variety of effects reported in the literature that arc observed when vanadium is added exogenously to enzymes, cells and tissues can be largely explained by consideration of the principles of aqueous inorganic vanadium chemistry. The true role of endogenous vanadium in living systems remains obscure, however.
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