Vanadium In Ascidians Research Articles

A Role for Vanadium in Ascidians and in Marine Algae

A Role for Vanadium in Ascidians and in Marine Algae

A non-oxo methanolate-bridged divanadium(IV) complex with tris(2-sulfanidylphenyl)phosphane ligands: synthesis, structural characterization and magnetic investigation.

Vanadium chemistry is of interest due its biological relevance and medical applications. In particular, the interactions of high-valent vanadium ions with sulfur-containing biologically important molecules, such as cysteine and glutathione, might be related to the redox conversion of vanadium in ascidians, the function of amavadin (a vanadium-containing anion) and the antidiabetic behaviour of vanadium compounds. A mechanistic understanding of these aspects is important. In an effort to investigate high-valent vanadium-sulfur chemistry, we have synthesized and characterized the non-oxo divanadium(IV) complex salt tetraphenylphosphonium tri-μ-<!?tlsb=-0.11pt>methanolato-κ(6)O:O-bis({tris[2-sulfanidyl-3-(trimethylsilyl)phenyl]phosphane-κ(4)P,S,S',S''}vanadium(IV)) methanol disolvate, (C24H20P)[V(IV)2(μ-OCH3)3(C27H36PS3)2]·2CH3OH. Two V(IV) metal centres are bridged by three methanolate ligands, giving a C2-symmetric V2(μ-OMe)3 core structure. Each V(IV) centre adopts a monocapped trigonal antiprismatic geometry, with the P atom situated in the capping position and the three S atoms and three O atoms forming two triangular faces of the trigonal antiprism. The magnetic data indicate a paramagnetic nature of the salt, with an S= 1 spin state.

Advances in research on the accumulation, redox behavior, and function of vanadium in ascidians.

The discovery of high levels of vanadium-containing compounds in ascidian blood cells goes back to 1911. Ascidians, which are also known as tunicates or sea squirts, belong to a subphylum of the Chordata, between the vertebrates and invertebrates. This discovery attracted the attention of an interdisciplinary group of chemists, physiologists, and biochemists, in part because of interest in the possible role of vanadium in oxygen transport as a prosthetic group in respiratory pigments, which was later shown not to be such a role, and in part because of the fact that high levels of vanadium were unknown in other organisms. The intracellular concentration of vanadium in some ascidian species can be as high as 350mm, which is 107 times that in seawater. Vanadium ions, which are thought to be present in the +5 oxidation state in seawater, are reduced to the +3 oxidation state via the +4 oxidation state and are stored in the vacuoles of vanadium-containing cells called vanadocytes, where high levels of protons and sulfate ions are also found. Recently, many proteins and genes that might be involved in the accumulation and reduction of vanadium have been isolated. In this review, we not only trace the history of vanadium research but also describe recent advances in our understanding of the field from several viewpoints: (i) vanadium-accumulating blood cells, (ii) the energetics of vanadium accumulation, (iii) the redox mechanism of vanadium, (iv) the possible role of sulfate, and (v) the physiological roles of vanadium.

Characterization of a novel vanadium-binding protein (VBP-129) from blood plasma of the vanadium-rich ascidian Ascidia sydneiensis samea

The ascidians, the so-called sea squirts, accumulate high levels of vanadium, a transition metal. Since Henze first observed this physiologically unusual phenomenon about one hundred years ago, it has attracted interdisciplinary attention from chemists, physiologists, and biochemists. The maximum concentration of vanadium in ascidians can reach 350 mM, and most of the vanadium ions are stored in the +3 oxidation state in the vacuoles of vanadium-accumulating blood cells known as vanadocytes. Many proteins involved in the accumulation and reduction of vanadium in the vanadocytes, blood plasma, and digestive tract have been identified. However, the process by which vanadium is taken in prior to its accumulation in vanadocytes has not been elucidated. In the present study, a novel vanadium-binding protein, designated VBP-129, was identified from blood plasma of the vanadium-rich ascidian Ascidia sydneiensis samea. Although VBP-129 mRNA was transcribed in all A. sydneiensis samea tissues examined, the VBP-129 protein was exclusively localized in blood plasma and muscle cells of this ascidian. It bound not only to VO2+ but also to Fe3+, Co2+, Cu2+, and Zn2+; on the other hand, a truncated form of VBP-129, designated VBP-88, bound only to Co2+, Cu2+ and Zn2+. In a pull-down assay, an interaction between VanabinP and VBP-129 occurred both in the presence and the absence of VO2+. These results suggest that VBP-129 and VanabinP function cooperatively as metallochaperones in blood plasma.

Vanadium-binding proteins (vanabins) from a vanadium-rich ascidian Ascidia sydneiensis samea

Since the beginning of the last century, it has been known that ascidians accumulate high levels of a transition metal, vanadium, in their blood cells, although the mechanism for this curious biological function remains unknown. Recently, we identified three vanadium-binding proteins (vanabins), previously denoted as vanadium-associated proteins (VAPs) [Zool. Sci. 14 (1997) 37], from the cytoplasm fraction of vanadium-containing blood cells (vanadocytes) of the vanadium-rich ascidian Ascidia sydneiensis samea. Here, we describe the cloning, expression, and analysis of the metal-binding ability of vanabins. Recombinant proteins of two independent but related vanabins, vanabin1 and vanabin2, bound to 10 and 20 vanadium(IV) ions with dissociation constants of 2.1×10 −5 and 2.3×10 −5 M, respectively. The binding of vanadium(IV) to these vanabins was inhibited by the addition of copper(II) ions, but not by magnesium(II) or molybdate(VI) ions. Vanabins are the first proteins reported to show specific binding to vanadium ions; this should provide a clue to resolving the problem regarding the selective accumulation of vanadium in ascidians.

Vanadocytes, cells hold the key to resolving the highly selective accumulation and reduction of vanadium in ascidians.

Since Henze discovered vanadium in the blood (or coelomic) cells of an ascidian in 1911, this unusual phenomenon has attracted the interest of many investigators. The highest concentration of vanadium (350 mM) in the blood cells of Ascidia gemmata, which belongs to the suborder Phlebobranchia, is 10(7) times higher than that in seawater. Of the approximately 10 types of blood cells, a combination of cell fractionation and neutron-activation analysis revealed that the signet ring cells were the true vanadocytes. In the vanadocytes, 97.6% of the vanadium is in the +3 oxidation state (III). The extremely low pH of 1.9 found in vanadocytes suggests that protons, concentrated by an H(+)-ATPase, might be linked to the accumulation of vanadium energetically. The antigen recognized by a monoclonal antibody, S4D5, prepared to identify vanadocytes, was determined to be 6-PGDH in the pentose phosphate pathway. NADPH produced in the pentose phosphate pathway in vanadocytes is thought to participate in the reduction of vanadium(V) to vanadium(IV). During embryogenesis, a vanadocyte-specific antigen first appears in the body wall at the same time that significant accumulations of vanadium become apparent. Three different vanadium-associated proteins (VAPs) were extracted from the blood cells of vanadium-rich ascidians. These are 12.5, 15, and 16 kDa in size and are associated with vanadium in an approximate ratio of 1:16. The cDNA encoding the 12.5 and 15 kDa VAPs was isolated and the proteins encoded were found to be novel. Further biochemical and biophysical characterization of the VAPs is in progress.

Physiological Function of Selective Accumulation of Vanadium in Ascidians from Sea Water and its Possible Application

Physiological Function of Selective Accumulation of Vanadium in Ascidians from Sea Water and its Possible Application

Hydrolytic species of V(H2O)63+ in relevance to the intracellular vanadium in ascidians

Hydrolytic species of V(H2O)63+ in relevance to the intracellular vanadium in ascidians

Vanadium in ascidians: Changes in vanadium coordination and oxidation state upon cell lysis

Changes in vanadium coordination during cell lysis have been followed by EPR spectroscopy of the blood cells of the phlebobranch ascidians Ascidia ceratodes and Phallusia julinea. The spectra obtained for A. ceratodes whole blood samples can be mainly ascribed to aquated oxovanadium(IV) in which the signals are broadened in freshly frozen blood relative to when the cells are lysed by thawing. The sources of this broadening are discussed and it is shown that the oxovanadium(IV) signal has its origin in a small percentage of damaged or lysed cells which release vanadium into a low sulfate, low acid environment in fresh samples. When thawed, the cells lyse releasing acid and sulfate into the environment of the oxovanadium(IV), with consequent narrowing of the EPR spectral linewidth. Freshly frozen P. julinea blood cell samples have EPR spectra with parameters intermediate between aquated oxovanadium(IV) and the “type I” parameters observed in a previous investigation of tissue samples of this species (S. G. Brand, C. J. Hawkins, A. T. Marshall, G. W. Nette, and D. L. Parry, Comp. Biochem. Physiol. 93B, 425 (1989)). A. ceratodes tissue samples also have EPR spectra that differ from that of the blood. It is suggested that EPR studies on tissue samples are more indicative of the resting state of vanadium in the cells as there is more physiological material to provide a pH buffering effect to stabilize the cells. Schemes are presented which incorporate all of the EPR observations in ascidian literature, where cellular lysis is proposed to be accompanied by vanadium undergoing oxidation and a series of chelate exchanges from a “type I” complex to aquated oxovanadium(IV). Protons released during these exchanges are suggested to provide the acidity characteristic of blood cell lysates. The biological implications of the concomitant release of vanadium and tunichrome (S. W. Taylor, D. L. Parry, C. J. Hawkins, and J. H. Swinehart, Comp. Biochem. Physiol. 106A, 531 (1993)) from the blood cells, to the process of wound repair are discussed.

Structure of triaqua(nitrilotriacetato)vanadium(III) tetrahydrate

Structure of triaqua(nitrilotriacetato)vanadium(III) tetrahydrate

Electrochemical investigation of V IV/V III/V II complexes- model studies for vanadium in ascidians

Electrochemical investigation of V IV/V III/V II complexes- model studies for vanadium in ascidians