Vanadium-binding protein in a vanadium-rich ascidian Ascidia sydneiensissamea: CW and pulsed EPR studies.
Some of the ascidians belonging to the suborder Phlebobranchia accumulate vanadium ion efficiently from seawater. Clarification of the mechanism of this surprisingly efficient metal-accumulation system is desirable. Two mutually similar vanadium-binding proteins (vanabin1 and vanabin2) have recently been isolated from a vanadium-rich ascidian Ascidia sydneiensis samea. In this study, the vanadium-binding properties of vanabin2 have been investigated by X-band CW EPR and pulsed EPR spectroscopy. CW EPR spectra of samples containing various ratios of VO2+ and vanabin2 invariably exhibited a usual mononuclear-type VO2+ EPR signal with the intensity dependent on the ratio [vanabin]/[V]. EPR titration has shown that vanabin2 can bind up to approximately 23.9 vanadium ions per one molecule, almost all of which ( approximately 84%) are in a mononuclear VO2+ state as estimated by EPR quantitation. Electron spin-echo envelope modulation (ESEEM) spectra of VO-vanabin2 exhibited reasonably intense peaks attributable to amine nitrogen. This is consistent with the fact that vanabin2 is a lysine-rich protein (14 lysines out of 91 amino acids). The present study reveals the uniqueness of vanabin2, which can bind a large number of metal ions in a mononuclear fashion in contrast to the situation for ferritin and metallothionein.
Fukui
Kôichi
K
Regional Joint Research Project of Yamagata Prefecture and Institute for Life Support Technology, YPCDI, Matsuei 2-2-1, Yamagata 990-2473, Japan. fukui@ckk.ymgt-techno.or.jp
Ueki
Tatsuya
T
Ohya
Hiroaki
H
Michibata
Hitoshi
H
D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D014561:Urochordata / Q000737:chemistry / Q000378:metabolism*; D014639:Vanadium / Q000737:chemistry / Q000378:metabolism*
D002352:Carrier Proteins; D014639:Vanadium