Sequence variation of Vanabin2-like vanadium-binding proteins in blood cells of the vanadium-accumulating ascidian Ascidia sydneiensis samea

Antioxidant and antidiabetic activities of vanadium binding proteins purified from the sea squirt Halocynthia roretzi

Sea squirts accumulate vanadium compounds with potent antidiabetic activity, which are involved in immune defense. In this study, vanadium concentrations of fresh blood plasma, intestine, and muscle of the sea squirt Halocynthia roretzi were 6.3, 3.7 and 2.1 mg/kg respectively. Two vanadium binding proteins (VBPs) from blood plasma and intestine were purified through (NH₄)₂SO₄ precipitation, and DEAE-Sepharose ion exchange and Sephacryl S-200 HR gel filtration chromatography, in that order. The purity and yield of the intestine and blood plasma vanadium binding proteins, VBP_intestine and VBP_{blood plasma,} were 13.4 folds and 7.1%, and 20.9 folds and 6.8%, respectively. There were two protein bands on the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) with molecular weights of 24.3 and 68.8 kDa and one with 96.7 kDa on the native-PAGE of VBP_{blood plasma}, whereas only one protein band of VBP_intestine on the SDS-PAGE with 26.5 kDa. Antioxidant activities of VBPs were lower than that of ascorbic acid. Both VBPs exerted strong inhibitory activity against Saccharomyces cerevisiae and mild against Bacillus stearothermophilus and rat intestinal α-glucosidase. IC₅₀ values of VBP_intestine and VBP_{blood plasma} against S. cerevisiae α-glucosidase were 28.34 and 12.60 μg/ml, respectively. The K_m , V_max , k_cat , and k_cat/K_m values of VBP_intestine and VBP_{blood plasma} were 4.29, 0.036, 6.58 and 1.53 × 10³, and 7.63 mM, 0.057 mM/min, 10.41 s^-1 and 1.36 × 10³ (M sec)^-1, respectively. There was a synergistic interaction between VBP_{blood plasma} and VBP_intestine on rat intestinal α-glucosidase inhibitory activity.

Assessment of total and organic vanadium levels and their bioaccumulation in edible sea cucumbers: tissues distribution, inter-species-specific, locational differences and seasonal variations

The objective of this study is to investigate the levels, inter-species-specific, locational differences and seasonal variations of vanadium in sea cucumbers and to validate further several potential factors controlling the distribution of metals in sea cucumbers. Vanadium levels were evaluated in samples of edible sea cucumbers and were demonstrated exhibit differences in different seasons, species and sampling sites. High vanadium concentrations were measured in the sea cucumbers, and all of the vanadium detected was in an organic form. Mean vanadium concentrations were considerably higher in the blood (sea cucumber) than in the other studied tissues. The highest concentration of vanadium (2.56 μg g(-1)), as well as a higher degree of organic vanadium (85.5 %), was observed in the Holothuria scabra samples compared with all other samples. Vanadium levels in Apostichopus japonicus from Bohai Bay and Yellow Sea have marked seasonal variations. Average values of 1.09 μg g(-1) of total vanadium and 0.79 μg g(-1) of organic vanadium were obtained in various species of sea cucumbers. Significant positive correlations between vanadium in the seawater and V org in the sea cucumber (r = 81.67 %, p = 0.00), as well as between vanadium in the sediment and V org in the sea cucumber (r = 77.98 %, p = 0.00), were observed. Vanadium concentrations depend on the seasons (salinity, temperature), species, sampling sites and seawater environment (seawater, sediment). Given the adverse toxicological effects of inorganic vanadium and positive roles in controlling the development of diabetes in humans, a regular monitoring programme of vanadium content in edible sea cucumbers can be recommended.

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 350 mm, which is 107times 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.