VANADIUM: A BIOLOGICALLY RELEVANT ELEMENT

This chapter focusses on the properties of the novel vanadium-containing bromoperoxidases. Vanadium has been shown to be an essential requirement in the biological systems and the chemistry of the element is gaining considerable interest. As the chemistry of vanadium is of direct relevance to the mechanism of action of bromoperoxidases, the chemistry of vanadate, properties of vanadium (V) complexes, and their reactivity, including reactions with peroxide, are discussed in the chapter. The work in three selected areas, vanadium in mushrooms, vanadium in oil and coal, and vanadium in tunicates, are also discussed in the chapter. Vanadium is also an essential element for some marine macro-algae, such as the brown seaweed F. spiralus and the green seaweed Enteromorpha compressa. Most assay methods to detect bromoperoxidase activity are based on the bromination of monochlorodimedone, a cyclic diketone that has high affinity for HOBr. The steady-state kinetics of the reaction of vanadium bromoperoxidase with hydrogen peroxide and bromide has been extensively studied. Hypobromous acid is known to be in rapid equilibrium with molecular bromine and tribromide ions in aqueous solutions. The first electron paramagnetic resonance (EPR) spectrum reported of an extract of the cap of the mushroom showed clearly an EPR signal characteristic of oxo-vanadium (IV). Tunicates, commonly called “sea squirts,” are very successful marine organisms found in all oceans of the world. © 1990 Academic Press Inc.