title: A novel vanadium reductase, Vanabin2, forms a possible cascade involved in electron transfer.
abstract: The unusual ascidian ability to accumulate high levels of vanadium ions at concentrations of up to 350 mM, a 10(7)-fold increase over that found in seawater, has been attracting interdisciplinary attention for a century. Accumulated V(V) is finally reduced to V(III) via V(IV) in ascidian vanadocytes. Reducing agents must therefore participate in the reduction. Previously, we identified a vanadium-binding protein, Vanabin2, in which all 18 cysteines form nine disulfide bonds. Here, we report that Vanabin2 is a novel vanadium reductase because partial cleavage of its disulfide bonds results in the reduction of V(V) to V(IV). We propose that Vanabin2 forms a possible electron transfer cascade from the electron donor, NADPH, via glutathione reductase, glutathione, and Vanabin2 to the acceptor, and vanadium ions conjugated through thiol-disulfide exchange reactions.
authors.affiliation: Department of Biological Science, Graduate School of Science, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima 739-8526, Japan.
authors.forename: Norifumi
authors.initials: N
authors.lastname: Kawakami
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Ueki
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Amata
authors.forename: Kan
authors.initials: K
authors.lastname: Kanamori
authors.forename: Koichi
authors.initials: K
authors.lastname: Matsuo
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Gekko
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Michibata