Toshiaki Ishii

Discovery of a new vanadium accumulator, the fan wormPseudopotamilla occelata

Many biologists, physiologists, and chemists have been interested in the significance of high vanadium concentrations in ascidians since the first report on its accumulation by Henze in 1911 [1]. In spite of many efforts to find other vanadium accumulators for a comparative study, it has been thought that only ascidians in the Animal Kingdom have the special ability to accumulate vanadium at a high level. During our screening work on elemental concentrations in marine organisms collected from the sea

Intracellular localization of vanadium in the fan worm Pseudopotamilla occelata

A very high level of vanadium was found to be contained in the polychaete worm Pseudopotamilla occelata collected in 1992–1993 from the Sanriku coast on the main island of Japan. The vanadium concentration (mean±SD=5500±1800 μg g-1 dry wt) in the worms branchial crown which is composed of many bipinnate radioles was approximately 100 times higher than that (mean±SD=60±25 μg g-1 dry wt) in the trunk body. Electron probe X-ray microanalysis revealed that a large amount of vanadium was present in the outer potion of the epidermis of the bipinnate radiole. Analytical electron microscopy for a cryo-section of the bipinnate radioles indicated that vanadium was localized in electron-dense deposits in the apical portion of epidermal cells. From an examination of the fine structures, the locality of the electron-dense deposits were found to correspond to that of the apical vacuoles in the epidermal cells. It was concluded that most of the vanadium in P. occelata was contained in the vacuoles of the epidermal cells of the bipinnate radioles.

XAFS Studies of Some Transition Elements Highly Accumulated in Seashells

XAFS analysis was used to reveal local atomic environment of manganese in the intracellular and extracellular granules from kidney tissues in several kinds of marine bivalves. The Mn K-absorption spectra of the kidney granules were measured in a fluorescence mode. The overall spectral shapes and the positions of the Mn K-absorption edge of the kidney granules of the bivalves are similar to each other and somewhat resemble those of eosphorite (MnAl(PO4)OH)2H2O) which contains Mn(II). These results, combined with those of IR analysis, suggest that manganese in the kidney granules exist as a phosphate with 6-fold coordination of oxygen atoms.

XAFS Studies of Vanadium in the Polychaete Worm Pseudopotamilla Occelata, a New Vanadium Accumulator

High accumulation of vanadium in P. occelata was recently discovered by the authors. The animal is a polychaete worm living in a clean sea and is the second vanadium accumulator in the Animal Kingdom, the ascidians being the first. XAFS analysis of the living animal disclosed that the vanadium was present as V(III) ions in a highly symmetrical octahedral coordination environment. This low oxidation state was stable only in a living state and it was easily oxidized in air to the V(IV) state if the sample was homogenized in an agate mortar or it was dried.