ABSTRACT
Vanadium occurs in biological systems primarily in the tetravalent and pentavalent forms. In body fluids at pH 4-8 the predominant forms of free vanadium are orthovanadates, HVO42 and H2VO4, where its oxidation state is 5. Once inside a cell it is reduced to the 4 state or vanadyl, i.e., VO2. Both oxidation states have similar biochemical and physiological function. Vanadate competes with phosphate for active sites in phosphate transport proteins, inhibiting the action of phosphates, and also has a pronounced inhibitory action on Na/K ATPase activity. As vanadyl, the metal competes with other transition metal ions for binding sites on metalloproteins (1). Vanadium is an essential nutrient for higher animals, including humans; it is present in mammalian tissues at concentrations below 1 mM, which was only recently determined with the advent of modern analytical techniques (2). A homeostatic mechanism maintains normal levels in the mammalian organism, and excess is rapidly excreted in the urine (3).
