Editing Vanadium (section)

=== Vanadium accumulation in tunicates ===
Vanadium is essential to [[tunicate]]s, where it is stored in the highly acidified [[vacuole]]s of certain blood cell types, designated [[vanadocyte]]s. [[Vanabins]] (vanadium-binding proteins) have been identified in the cytoplasm of such cells. The concentration of vanadium in the blood of [[Ascidiacea|ascidian]] tunicates is as much as ten million times higher{{specify|date=April 2014}}<ref>{{cite journal |last1=Smith |first1=M. J. |date=1989 |title=Vanadium biochemistry: The unknown role of vanadium-containing cells in ascidians (sea squirts) |journal=Experientia |volume=45 |issue=5 |pages=452–7 |doi=10.1007/BF01952027 |pmid=2656286 |s2cid=43534732}}</ref><ref>{{cite journal |last1=MacAra |first1=Ian G. |last2=McLeod |first2=G. C. |last3=Kustin |first3=Kenneth |date=1979 |title=Tunichromes and metal ion accumulation in tunicate blood cells |journal=Comparative Biochemistry and Physiology B |volume=63 |issue=3 |pages=299–302 |doi=10.1016/0305-0491(79)90252-9}}</ref> than the surrounding seawater, which normally contains 1 to 2&nbsp;μg/L.<ref>{{cite journal |last1=Trefry |first1=John H. |last2=Metz |first2=Simone |date=1989 |title=Role of hydrothermal precipitates in the geochemical cycling of vanadium |journal=Nature |volume=342 |issue=6249 |pages=531–533 |bibcode=1989Natur.342..531T |doi=10.1038/342531a0 |s2cid=4351410}}</ref><ref>{{cite journal |last1=Weiss |first1=H. |last2=Guttman |first2=M. A. |last3=Korkisch |first3=J. |last4=Steffan |first4=I. |date=1977 |title=Comparison of methods for the determination of vanadium in sea-water |journal=Talanta |volume=24 |issue=8 |pages=509–11 |doi=10.1016/0039-9140(77)80035-0 |pmid=18962130}}</ref> The function of this vanadium concentration system and these vanadium-bearing proteins is still unknown, but the vanadocytes are later deposited just under the outer surface of the tunic, where they may deter [[predation]].<ref>{{cite book |last1=Ruppert |first1=Edward E. |title=Invertebrate Zoology |last2=Fox |first2=Richard, S. |last3=Barnes |first3=Robert D. |date=2004 |publisher=Cengage Learning |isbn=978-81-315-0104-7 |edition=7th |pages=947}}</ref>