Ascidians vanadium

In the case of the sea squirts (ascidians), vanadium plus sulfur XAS studiesl" ]... 

Other studies investigated marine animals such as ascidia (subtype of Ttini-cata ) and holothurians (type Echinodermata ). Peterson [8] is only one of the many authors that have pointed out the high vanadium concentrations common in ascidians [7]. These animals contain 10,000 times the vanadium that is present in the water in which they live [5]. In ascidians, special green blood cells called vanadocytes concentrate the element. Vanadium in these cells is in the trivalent state, is complexed to pyrrole rings, and is associated with unusually high concentrations of sulfuric acid [4]. In other ascidians, vanadium is concentrated in the blood plasma (hemovanadium) rather than in individual cells. Although the vana-... 

Certain vertebrates have an astonishing ability to accumulate vanadium in their blood. For example, the ascidian seaworm Phallusia mammilata has a blood concentration of V up to 1900 ppm, which represents more than a millionfold concentration with respect to the sea-water in which it lives. The related organism Ascidia nigra has an even more spectacular accumulation with concentrations up to 1.45% V (i.e. 14 500 ppm) in its blood cells, which also contain considerable concentrations of sulfuric acid (pH 0). One possibility that has been mooted is that the ascidia accumulates vanadate and polyvanadate ions in mistake for phosphate and polyphosphates (p. 528). 

Figure 17.16 Model of the pathway for reduction and accumulation of vanadium in ascidian vanadocytes. (From Crans et al., 2004. Copyright (2004) American Chemical Society.)...

Tunicates (ascidians or sea-squirts) are invertebrate marine organisms, which can accumulate vanadium at concentrations approaching 350 mM (the concentration of vanadium in seawater is 10 8 M). This vanadium is taken up as V(V) from seawater (Figure 17.16), reduced to oxidation state III or IV and stored in a soluble form in the blood cells within acidic vacuoles at concentrations a million fold higher than in their external surroundings. 

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... 

Although die role of iron in various heme derivatives and zinc in carboxypep-tidase and carbonic anhydrase is dear. Ihere are many instances in which little is known of the function of the trace metal. For example, it has been known for some time that ascidians ("sea squirts") concentrate vanadium from sea water by a factor of a millionfold, but a satisfactory explanation for its role in these animals remains elusive.117 There are many elements that are known to be usefol but for which no specific function has yet been proved. The list of known functions is expanding rapidly, however. 

The ascidians or tunicates (sea squirts) accumulate vanadium from seawater (about 5x 10-8 mol dm-3) to a level of about 1 mol dm-3 and store it in a dilute solution of sulfuric acid (pH<2) in blood cells called vanadocytes. The tunicates thus concentrate vanadium several million-fold. 079 NMR, ESR and EXAFS determinations on whole vanadocyte cells of Ascidia ceratodes and Ascidia nigra indicate that the vanadium is present mainly as aquated V111 probably complexed with sulfate. Some vanadyl ion (5-10%) is also present.1080 1081... 

Tullius, T.D., Gillum, W.O., Carlson, R.M.K. and Hodgson, K.O. (1980) Structural study of the vanadium complex in living Ascidian blood cells by X-ray absorption spectroscopy./. Am. Chem. Soc. 102, 5670-5677. 

The tunichromes constitute a class of amino-acid-derived metabolites isolated from the blood cells of ascidians. The chemicals are involved in vanadium sequestration and reduction in the blood cells and may be involved in a primitive clotting mechanism to repair damaged tissue.226-227 The... 

Examples of secondary metabolites from Ascidians are shown in Figure 3.10. Ascidians are noteworthy for the presence of vanadium (and related metals) together with high concentrations of sulphuric acid and tunichromes, which are unstable hydroquinoid compounds. A defensive role for these has been suspected,98 and it is noteworthy that gastropod molluscs (both prosobranch and opisthobranch) that feed upon tunicates often secrete large amounts of sulfuric acid, used in both... 

Ueki, T., N. Yamaguchi, and H. Michibata. 2003. Chloride channel in vanadocytes of a vanadium-rich ascidian Ascidia sydneiensis samea. Comp. Biochem. Physiol. B Biochem. Mol. Biolog. 136 91-98. 

Michibata, H., T. Uyama, and K. Kanamori. 1998. The accumulation mechanism of vanadium by ascidians. In Vanadium compounds. Chemistry, biochemistry and therapeutic applications, A.S. Tracey and D.C. Crans (Eds.), American Chemical Society, Washington, D.C., pp. 248-258. 

Kanamori, K. 2003. Structures and properties of multinuclear vanadium(III) complexes Seeking a clue to understand the role of vanadium(IB) in ascidians. Coord. Chem. Rev. 237 147-161. 

Michibata, H., N. Yamaguchi, T. Uyama, and T. Ueki. 2003. Molecular biological approaches to the accumulation and reduction of vanadium by ascidians. Coord. Chem. Rev. 237 41-51. 

Hamada, T., M. Asanuma, T. Ueki, F. Hayashi, N. Kobayashi, S. Yokoyama, H. Michibata, and H. Hirota. 2005. Solution structure of vanabin2, a vanadium(IV)-binding protein from the vanadium-rich ascidian Ascidia sydneiensis samea. J. Am. Chem. Soc. 127 4216-4222. 

Yamaguchi, N., K. Kamino, T. Ueki, and H. Michibata. 2004. Expressed sequence tag analysis of vanadocytes in a vanadium-rich ascidian, Ascidia sydneiensis samea. Marine Biotech. 6 165-174. 

GSH has been proposed to be part of the thiol cycling in mammalian cells that may transduce oxidative stress redox signaling into the induction of many genes involved in proliferation, differentiation, and apoptosis [15], Studies with pure chemical systems have confirmed the reduction of V(V) maltol compounds by GSH or ascorbic acid [16], Putative glutathione transferase enzymes that bind vanadium have been isolated from an ascidian that accumulates vanadium in specialized cells to over 350 mM [17],... 

Ascidians or tunicates (Phylum Chordata) belong to the class of Ascidiacea and are common marine animals whose body is enclosed in a jacket or tunic. The animals are attached to rocks and are either solitary or colonial. They continuously filter seawater to obtain minute organisms and particulate organics. As was originally discovered by Henze the animals concentrate vanadium from seawater to levels about 10 times that present in seawater (35 nM), a phenomenon that has attracted considerable interest. The transition metal is present... 

Fig. 4. Frequently cited ascidian blood cell types. The middle column refers to staining properties of each type of cell with the two reagents osmium tetroxide and the pH indicator neutral red. Free tunichrome would reduce osmium tetroxide, as would lower oxidation states of vanadium.

It should also be noted that ova of ascidians, unusual in containing somatic cells from the parent organism, are quite high in vanadium... 

The occurrence of vanadium in the lower oxidation states, which as the simple aqua ions undergo acid dissociation above pH 3 [if present as V(III)) ] and pH 6 [in the case of oxo-V(IV) ], along with the high sulfur content of ascidian blood and the low pH that results when ascidian blood cells are ruptured in distilled water has led to the belief that intact vanadium-containing tunicate blood cells are acidic (145). Other lines of evidence, including vital staining and NMR (144,170), and... 

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