- Model studies related to vanadium biochemistry: recent advances and perspectives

The biological effects, biodistribution and toxicology of vanadium, such as its requirement and pharmacological activity, are areas of increasing research interest. Although numerous biochemical and physiological functions have been suggested for this element, and despite the amount of the knowledge so far accumulated, vanadium still does not have a clearly defined role in the higher forms of life.1-5

The best evidence for a biological role of vanadium comes from bacteria (the so-called alternative nitrogenases in which vanadium replaces molybdenum in the FeMo-cofactor of some Azotobacter species)4-7 and from plants (vanadium- dependent haloperoxidases found in some algae, lichens and fungi).4,5,8,9

On the other hand, experiments with laboratory animals have shown that vanadium deprivation enhances abortion rates, reduces milk levels during lactation and produces thyroidal disorders. Other evidence points to the possible role of vanadium in the regulation of ATP-ases, phosphoryl transfer enzymes, adenylate cyclase, and protein kinases. However, many actions of vanadium can be also explained by its having a role similar to, or enhancing recently described growth factors such as the epidermal growth factor, the fibroblast growth factor and even insuline.10

Like molybdenum, vanadium occupies an exceptional position among the bioelements because both, anionic and cationic forms can participate in biological processes.3,5,11,12 In its anionic forms (vanadates(V)), it resembles phosphates, but in its cationic forms - mainly as VO2+ - it behaves like a typical transition metal ion, which competes with other metal cations in coordination with biogenic ligands or compounds. This duality, together with the facility with which it changes oxidation states and coordination environments, may be responsible for the very peculiar and somewhat unparalleled behavior of this biometal.5,12

Aspects of the coordination chemistry of vanadium relevant to its presence and activity in biological systems have been recently reviewed.2-4,11-14 In this account we will present some of our recent results of studies on model systems related to aspects of the biochemistry of vanadium and those of other research groups working in this field.

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