RESEARCH FOR METAL-BINDING ABILITY AND SELECTIVITY OF VANADIUM-BINIDNG PROTEIN FROM ASCIDIANS

生活在海洋中的被囊动物从海水中积累钒(V)离子，并以钒(III)离子的形式储存在它们的血细胞中。然而，这一独特的钒积累和还原机制尚未被探索。在本课题中，我们利用钒结合蛋白及其小分子模型化合物，获得了关于被囊动物血细胞中钒的积累和还原的基本知识。1.NADPH将钒(V)还原为钒(IV)：NADPH可能参与了被囊动物对钒(V)的还原。我们已经报道了在EDTA存在下，NADPH可以将钒(V)还原为钒(IV)。在本项目中，我们研究了氨基酸和多肽对NADPH还原钒(V)的促进作用。我们发现，能够以三齿配基形式与钒结合的氨基酸和多肽可以促进还原，而那些只能以双齿形式与钒结合的氨基酸和多肽则不能。2.硫醇还原钒(IV)为钒(III)：我们发现在EDTA存在下，半胱氨酸甲酯能促进钒(IV)还原为钒(III)。我们发现，NTA、甘氨酸组氨酸和甘氨天冬氨酸也能促进钒(IV)的还原，但有部分促进作用。富含钒结合蛋白的赖氨酸残基似乎与钒(V)和钒(IV)的还原无关。3.钒(III)氧化钒结合蛋白：为了研究钒(III)能否还原二硫键，我们研究了钒(III)与胱氨酸或谷胱甘肽(氧化形式)的反应。我们发现，模型化合物中的二硫键被钒(III)断裂。钒(III)对钒结合蛋白的还原作用正在研究中。

Tunicates living in sea accumulate vanadium(V) ion from sea water and stores in their blood cells as vanadium(III) ion. However, this unique mechanism for vanadium accumulation and reduction has not been explored. In this project, we have obtained the basic knowledge concerning the vanadium in tunicates blood cells in order to explore the mechanism of accumulation and reduction of vanadium, using vanadium-binding protein and its small molecular model compounds.1.Reduction of vanadium(V) to vanadium(IV) by NADPH : It has been suggested that NADPH might be involved in the reduction of vanadium(V) by tunicates. We have already reported NADPH can reduce vanadium(V) to vanadium(IV) in the existence of edta. In this project, we have studied whether amino acids and peptide can act as a promoter of the reduction of vanadium(V) by NADPH. We have found that amino acids and peptides that can bind to vanadium as a tridentate ligand can promote the reduction while those that can bind to vanadium only as a bidentate fashion can not.2.Reduction of vanadium(IV) to vanadium(III) by thiol : We have shown that cystein methyl ester can promote the reduction of vanadium(IV) to vanadium(III) in the presence of edta. We have found that nta, glycylhistidine, and glycylaspartic acid can also promote the reduction of vanadium(IV) though partly. Lysine residue, which is rich in vanadium-binding protein, does not seem to relate to the reduction of vandium(V) and (IV).3.Oxidation of vanadium-binding protein by vanadium(III) : In order to examine whether the dithio bond can be reduced by vanadium(III), we examined the reaction between vanadium(III) and cystine or glutathione (oxidiazed form) as a model compound of vanadium-binding protein. We found that the dithio bond in the model compounds was cleaved by vanadium(III). The reduction of vanadium-binding protein by vanadium(III) is now under investigation.