Identification of a vanadium-associated protein from the vanadium-rich ascidian, Ascidia sydneiensis samea

Ascidians are known to accumulate vanadium in their blood cells (vanadocytes) at extremely high levels which correspond to about 10⁶ to 10⁷ times the levels of vanadium ions in seawater. The route for the accumulation of vanadium ions from the outside environment into the blood system in ascidians has not yet been discovered. In the present experiments, using a combined technique of anion exchange column and atomic absorption spectrometry, we first extracted a vanadium-associated protein (VAP) from the blood cells of the ascidian Ascidia sydneiensis samea. VAP was estimated to associate with vanadium at an approximate ratio of 1 mol : 16 mols. SDS-PAGE and a polyclonal antibody against VAP (anti-VAP) revealed that VAP is composed of at least two types of peptides estimated to be 12.5 kDa and 15 kDa with a minor peptide of 16 kDa and that VAP is localized in the cytoplasm of the vanadocytes.