Publisher Summary 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.

Vanadium : a biologically relevant element

https://ir.lib.hiroshima-u.ac.jp/files/public/0/21/20141016115441728229/CoordChemRev_234_41-51_2003.pdf

Molecular biological approaches to the accumulation and reduction of vanadium by ascidians

Metals are essential cofactors for bio‐chemical processes, including oxidative phosphorylation, gene regulation and free‐radical homeostasis. Abnormalities in metal ions concentration in organisms, lead towards the eco‐physiological hazards in the aquatics. In aquatic organisms, metal absorption involves transfer of metals to the circulatory system following : uptake by the apical membrane; movement through the cell as well as interaction with intracellular ligands and efflux across the basolateral membrane. Sequestration of metals in an immobilized form occurs throughout the various tissues and organs involved in pathways for metal uptake, transport, utilization and release. Metallothioneins, metal binding proteins, regulate the essential metals (Cu, Zn), detoxify the toxic metals (Cd, Hg) and play key role to the sequestering metals. Plasma proteins play the central role in metal transport in the vertebrates. Besides, blood cells in aquatic invertebrates, hemocytes in mollusks concentrate a variety of m...

Metals in aquatic ecosystems: mechanisms of uptake, accumulation and release‐Ecotoxicological perspectives

Ascidian blood cells contain a level of vanadium ion much higher than that in seawater. Blood cells are generally classified into six to nine types based on their morphology. On the basis of a Ficoll gradient for cell fractionation, neutron activation analysis of vanadium ion, and ESR spectra of oxovanadium ion in blood cells, the signet ring cells are the most likely “vanadocytes” in Ascidia ahodori. The vanadyl ion (VO2+), detected in high levels in these cells, binds with some low molecular weight substances through their oxygen donors.

Separation of vanadocytes: Determination and characterization of vanadium ion in the separated blood cells of the ascidian, Ascidia ahodori

Unraveling the chemistry of tunichrome

The vanadium, iron, and manganese contents of 15 species of solitary ascidians belonging to the suborders Phlebobranchia and Stolidobranchia were determined by thermal neutron activation analysis. Vanadium was detectable in all species examined. In general, the vanadium content in various tissues of the Phlebobranchia was considerably higher than the iron and manganese contents. The blood cells especially contained a large amount of vanadium. The highest value (21 µg vanadium/mg dry weight) was obtained from blood corpuscles of Ascidia ahodori. Species in the suborder Stolidobranchia, on the other hand, had smaller quantities of vanadium in comparison with those in the suborder Phlebobranchia. The iron and manganese contents did not differ greatly between the two suborders. The data are considered in the light of physiological roles of these transition metals in ascidians.

T. Terada

Papers

The accumulation and distribution of vanadium, iron, and manganese in some solitary ascidians