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ID 21
file
creator
Michibata, Hitoshi
Yamaguchi, Nobuo
Uyama, Taro
subject
Ascidian
Tunicate
Vanadium
Accumulation
Reduction
Metalbinding protein
NDC
Chemistry
abstract
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.
journal title
Coordination chemistry reviews
volume
Volume 237
issue
Issue 1-2
start page
41
end page
51
date of issued
2003
publisher
Elsevier Science B.V.
issn
0010-8545
publisher doi
language
eng
nii type
Journal Article
HU type
Journal Articles
DCMI type
text
format
application/pdf
text version
author
rights
Copyright (c) 2002 Elsevier Science B.V.
relation is version of URL
http://dx.doi.org/10.1016/S0010-8545(02)00278-3
department
Graduate School of Science