Vanadium accumulation

The sea squirts or tunicates are fascinating marine creatures, their name being derived from the tunic made of cellulosic material that surrounds the body of the animal. In 1911, Henze discovered vanadium in the blood of Phallusia mammillata C.343 He later found the same with other ascidians (a class of tunicates). In vanadium-accumulating species, most vanadium is located in the vacuoles—vanadophores—of certain types of blood cells—the vanadocytes. The concentration in the vanadophore can be as high as 1M and this value must be compared with concentrations of the order of 2 x 10-8 M for vanadium in sea water.344 Kustin et al. have reviewed the work done to understand the efficient accumulation and the possible biological roles of the metal.345... 

Figure 14 Mechanism of vanadium accumulation in the vanadophore assuming a membrane permeable only to anions...

It may be there to poison predators.614 The vanadium-accumulating species also synthesize several complex, yellow catechol-type chelating agents (somewhat similar to enterobactin Fig. 16-1) which presumably complex V(V) and perhaps also reduce it to V(III).615 Vanadium is also accumulated by other marine organisms and by the mushroom Amanita muscaria. 

Vanadium accumulates in some species of Amanita toadstools (Frausto da Silva, 1989). Amavadine, the vanadium containing substance, is discussed in Chapter 9. 

In order to interpret the relationship obtained between the apparent kinetic constants and the amount of vanadium accumulated on the catalysts (Figures 5 and 6), a simple model was developed. 

The influx of vanadate is a rapid (t1/2 = 57 s at 0°C), monophasic process85, but the rate of vanadate influx approaches a saturation limit at high concentrations of exogenous vanadate. Influx experiments with added EDTA (ethylenediamminetetraacetic acid) were carried out to eliminate exchange or adhesion of vanadate to the cell surface to account for the reduction of radiovanadium in the extracellular medium. The amount of vanadium accumulated in a typical influx experiment was independent of added EDTA, and raised the intracellular concentration by 2.5 mM. Therefore, there is a net uptake of vanadium into the intracellular volume of the vanadocytes in these experiments. 

Figure 1. Vanadium accumulation during ETM as a function of time on stream. Target 5000 ppm on catalyst...

Breit G. N. and Wanty R. B. (1991) Vanadium accumulation in carbonaceous rocks a review of geochemical controls during deposition and diagenesis. Chem. Geol. 91, S3-91. 

Seefeldt, L. C., Hoffman, B. M., Dean, D. R. (2009). Mechanism of Mo-dependent nitrogenase. The Annual Review ofBiochemistry, 78,701—722. Ueki, T, Furano, N., Michibata, H. (2011). A novel vanadium transporter of the Nramp family expressed at the vacuole of vanadium-accumulating cells of the ascidian Ascidia sydneiensis samea Biochimica et Biophysica Acta, 1810, 457—464. 

M. manhattensis does not, however, accumulate vanadium. No appreciable reduction to V was found with the tunichrome from A nigra, an effective vanadium accumulator (Table 4.1). On the other hand, reaction of [VO(acac)2] with 2,4-di(fert-butyl)catechol yields [V(semiquinone)3]. 

Domingo JL, Gomez M, Sanchez DJ, Llobet JM, Keen CL. 1995. Toxicology of vanadium compounds in diabetic rats the action of chelating agents on vanadium accumulation. Mol Cell Biochem 153 233—240. 

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