Ascidians blood

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. 

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.

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... 

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). 

Hawkins, C.J., D.L. Parry, and C. Pierce. 1980. Chemistry of the blood of the ascidian Podoclavella moluc-censis. Biol. Bull. 159 669-680. 

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. 

Webb, D. A., Observations on the blood of certain ascidians, with special... 

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... 

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... 

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... 

Yoshihara, M., T. Ueki, T. Watanabe, N. Yamaguchi, K. Kamino, and H. Michibata. 2005. VanabinP, a novel vanadium-binding protein in the blood plasma of an ascidian, Ascidia sydneiensis samea. Biochim. Biophys. Acta 1730 206-214. 

Vanadium occurs in a few biological systems, and particularly in the blood of a group of sea creatures (Ascidians) where it may function as an... 

Vanadium has long been recognized as a biologically active metal which has an important metabolic role in various marine organisms 53). A vanadium concentration 5 x 105 times that found in natural sea water has been reported in the blood of the ascidian Phallusia mamillata 57). Vanadium is concentrated in form of the blood pigment hemovanadium58). Moreover, vanadium enrichment factors of 4500 in scallops, 2500 in mussels, and 1500 in oysters were observed 59). 

At this point I would like to thank Kenneth Kustin, who helped me a lot in tracing back (historical) facts on tile blood of ascidians. 

The role of vanadium in the blood of ascidians remains elusive. An interesting hypothesis was proposed by Smith almost three decades ago, ] namely that the low oxidation state of vanadium and the low pH are the result of an... 

The early suggestion of Henze, according to which also in the chemistry laboratory represented by the cell, this [vanadium] compound may infer oxidations, may or may not be correct, a suggestion which was based on the (even at that time) well-established ability of vanadic acid to catalyse oxidations, e.g. aniline to aniline black. Almost three decades later, Webb stated in an article on Observations on the blood of certain ascidians ] It may be confessed at the start that it has been found impossible to suggest any plausible explanation of the function of the vanadium compound, and that only a little progress has been made towards elucidating its chemical namre . The chemical nature of haemovanadin nowadays is well established, but with respect to its function we are no better off than we were almost 100 years ago. 

Vanadium(III) in Phlebobranchia ascidians with a high acidity in the signet ring cell vacuoles (e.g. Ascidia gemmata) makes up about 98% of the overall vanadium present in blood cells. The V ratio decreases with increasing pH. According to magnetic... 

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