Molecular biological approaches to the accumulation and reduction of vanadium by ascidians

About 90 years ago, Henze discovered high levels of vanadium in the blood (coelomic) cells of an ascidian collected from the Bay of Naples. His discovery attracted the interdisciplinary attention of chemists, physiologists, and biochemists. Two decades ago, we quantified the vanadium levels in several ascidian tissues definitively using neutron-activation analysis and revealed that some species in the family Ascidiidae accumulate vanadium at concentrations in excess of 350 mM, corresponding to about 107 times that found in seawater. Vanadium accumulated is reduced to the +3 oxidation state via the +4 oxidation state and stored in vacuoles of vanadocytes (vanadium-containing blood cells) where high levels of protons and sulfate are also contained. To investigate this unusual phenomenon, we isolated several proteins and genes that are expressed in vanadocytes. To date, three types of vanadium-binding protein, designated as Vanabins, have been isolated, with molecular masses of 12.5, 15, and 16 kDa, along with the cDNAs encoding these proteins. In addition, four types of enzyme related to the pentose phosphate pathway that produces NADPH were revealed to be located in vanadocytes. The pentose phosphate pathway participates in the reduction of vanadium(V) to vanadium(IV). The cDNA for each of the vacuolar-type H+-ATPase (V-ATPase) A, B, C, and D subunits, which are located on the vacuolar membranes of vanadocytes, has been isolated and analyzed. V-ATPase generates a proton-motive force, and is thought to provide the energy for vanadium accumulation.To clarify the entire mechanism involved in the accumulation and reduction, much more genes and proteins expressed in the blood cells need to be systematically identified. Thus, we have performed an expressed sequence tag (EST) analysis of blood cells and have established the functional assay system to elucidate the functions of genes and proteins obtained from ascidian blood cells

Subunit C of the Vacuolar-Type ATPase from the Vanadium-Rich Ascidian, Ascidia sydneiensis samea, Rescued the pH Sensitivity of Yeast vma5 Mutants

A vanadium-accumulating ascidian, Ascidia sydneiensis samea, expresses vacuolar-type H+-ATPases (V ATPases) on the vacuole membrane of the vanadium-containing blood cells known as vanadocytes. Previously, we showed that the contents of their vacuoles are extremely acidic and that a V ATPase-specific inhibitor, bafilomycin A1, neutralized the contents of the vacuoles. To understand the function of V ATPase in vanadocytes, we isolated cDNA encoding subunit C of V ATPase from vanadocytes since this subunit has been known to be responsible for the assembly of V-ATPases and to regulate the ATPase activity of V-ATPases. The cloned cDNA was 1,443 nucleotides in length, and encoded a putative 384 amino-acid protein. By expressing the ascidian cDNA for subunit C under the control of a galactose-inducible promoter, the pH-sensitive phenotype of the corresponding vma5 mutant of a budding yeast was rescued. This result showed that the ascidian cDNA for subunit C functioned in yeast cells

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 107 times higher than that in sea water. Of the approximately ten 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, 97.60f 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 as 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

Exclusive Expression of Transketolase in the Vanadocytes of the Vanadium-Rich Ascidian, Ascidia sydneiensis samea

Ascidians, especially those belonging to the Ascidiidae, are known to accumulate extremely high levels of vanadium in vanadocytes, one type of blood (coelomic) cell. Vanadium, which exists in the +5 oxidation state in seawater, is accumulated in the vanadocytes and reduced to the +3 oxidation state. We have been trying to characterize all of the polypeptides specific to vanadocytes and to specify the proteins that participate in the accumulation and reduction of vanadium. To date, we have localized three enzymes in vanadocytes: 6-phosphogluconate dehydrogenase (6-PGDH: EC 1.1.1.44), glucose-6-phosphate dehydrogenase (G6PDH: EC 1.1.1.49), and glycogen phosphorylase (GP: EC 2.4.1.1), all of which are involved in the pentose phosphate pathway. In the current study, we cloned a cDNA for transketolase, an essential and rate-limiting enzyme in the non-oxidative part of the pentose phosphate pathway, from vanadocytes. The cDNA encoded a protein of 624 amino acids, which showed 61.8 0dentity to the human adult-type transketolase gene product. By immunocytochemistry and immunoblot analyses, the transketolase was revealed to be a protein that was expressed only in vanadocytes and not in any of the more than ten other types of blood cell. This finding, taken together with the localized expression of the other three enzymes, strongly supports the hypothesis that the pentose phosphate pathway functions exclusively in vanadocytes

Subaru/HiCIAO HKsHK_{\rm s} imaging of LkHα\alpha 330 - multi-band detection of the gap and spiral-like structures

We present $H$- and $K_{\rm s}$-bands observations of the LkH$\alpha$ 330 disk with a multi-band detection of the large gap and spiral-like structures. The morphology of the outer disk ($r\sim$0\farcs3) at PA=0--45$^\circ$ and PA=180--290$^\circ$ are likely density wave-induced spirals and comparison between our observational results and simulations suggests a planet formation. We have also investigated the azimuthal profiles at the ring and the outer-disk regions as well as radial profiles in the directions of the spiral-like structures and semi-major axis. Azimuthal analysis shows a large variety in wavelength and implies that the disk has non-axisymmetric dust distributions. The radial profiles in the major-axis direction (PA=$271^\circ$) suggest that the outer region (r\geq0\farcs25) may be influenced by shadows of the inner region of the disk. The spiral-like directions (PA=10$^\circ$ and 230$^\circ$) show different radial profiles, which suggests that the surfaces of the spiral-like structures are highly flared and/or have different dust properties. Finally, a color-map of the disk shows a lack of an outer eastern region in the $H$-band disk, which may hint the presence of an inner object that casts a directional shadow onto the disk.Comment: 12pages, 16 figures, 2 tables, accepted for publication in A

SUBARU Near-Infrared Imaging Polarimetry of Misaligned Disks Around The SR24 Hierarchical Triple System

The SR24 multi-star system hosts both circumprimary and circumsecondary disks, which are strongly misaligned from each other. The circumsecondary disk is circumbinary in nature. Interestingly, both disks are interacting, and they possibly rotate in opposite directions. To investigate the nature of this unique twin disk system, we present 0.''1 resolution near-infrared polarized intensity images of the circumstellar structures around SR24, obtained with HiCIAO mounted on the Subaru 8.2 m telescope. Both the circumprimary disk and the circumsecondary disk are resolved and have elongated features. While the position angle of the major axis and radius of the NIR polarization disk around SR24S are 55$^{\circ}$ and 137 au, respectively, those around SR24N are 110$^{\circ}$ and 34 au, respectively. With regard to overall morphology, the circumprimary disk around SR24S shows strong asymmetry, whereas the circumsecondary disk around SR24N shows relatively strong symmetry. Our NIR observations confirm the previous claim that the circumprimary and circumsecondary disks are misaligned from each other. Both the circumprimary and circumsecondary disks show similar structures in $^{12}$CO observations in terms of its size and elongation direction. This consistency is because both NIR and $^{12}$CO are tracing surface layers of the flared disks. As the radius of the polarization disk around SR24N is roughly consistent with the size of the outer Roche lobe, it is natural to interpret the polarization disk around SR24N as a circumbinary disk surrounding the SR24Nb-Nc system.Comment: 14 pages, 5 figures, accepted for publication in A

Vanadium-containing blood cells (vanadocytes) show no fluorescence due to the tunichrome in the ascidian, Ascidia sydneiensis samea : Biochemistry

Volume: 7Start Page: 55End Page: 6