Editing Tungsten (section)

==Biological role==
Tungsten, at atomic number ''Z'' = 74, is the heaviest element known to be biologically functional. It is used by some bacteria and [[archaea]],<ref>{{cite journal| title = Identification of molybdopterin as the organic component of the tungsten cofactor in four enzymes from hyperthermophilic Archaea | vauthors = Johnson JL, Rajagopalan KV, Mukund S, Adams MW | journal = [[Journal of Biological Chemistry]] |date = 5 March 1993 |volume =268 |issue=7 | pages = 4848–52| doi = 10.1016/S0021-9258(18)53474-8 |pmid= 8444863 | doi-access = free }}</ref> but not in [[eukaryotes]]. For example, [[enzyme]]s called [[oxidoreductase]]s use tungsten similarly to [[molybdenum]] by using it in a tungsten-[[pterin]] complex with [[molybdopterin]] (molybdopterin, despite its name, does not contain molybdenum, but may complex with either molybdenum or tungsten in use by living organisms). Tungsten-using enzymes typically reduce carboxylic acids to aldehydes.<ref name="tungsten_orgs">{{cite book|last=Lassner|first=Erik|title=Tungsten: Properties, Chemistry, Technology of the Element, Alloys and Chemical Compounds|publisher=Springer|date=1999|pages=409–411|isbn=978-0-306-45053-2|url=https://books.google.com/books?id=foLRISkt9gcC&pg=PA409}}</ref> The tungsten oxidoreductases may also catalyse oxidations. The first tungsten-requiring enzyme to be discovered also requires selenium, and in this case the tungsten-selenium pair may function analogously to the molybdenum-sulfur pairing of some molybdopterin-requiring enzymes.<ref>{{cite journal| url = http://media.iupac.org/publications/pac/1998/pdf/7004x0889.pdf| title = Transition metal sulfur chemistry and its relevance to molybdenum and tungsten enzymes| author = Stiefel, E. I.| journal = Pure Appl. Chem.| volume = 70| issue = 4| pages = 889–896| date = 1998| doi = 10.1351/pac199870040889| url-status = live| archive-url = https://web.archive.org/web/20081203120549/http://media.iupac.org/publications/pac/1998/pdf/7004x0889.pdf| archive-date = 2008-12-03| citeseerx = 10.1.1.614.5712| s2cid = 98647064}}</ref> One of the enzymes in the oxidoreductase family which sometimes employ tungsten (bacterial [[formate dehydrogenase]] H) is known to use a selenium-molybdenum version of molybdopterin.<ref>{{cite journal|doi=10.1021/bi972177k |title=Selenium-Containing Formate Dehydrogenase H from Escherichia coli: A Molybdopterin Enzyme That Catalyzes Formate Oxidation without Oxygen Transfer|journal= Biochemistry|date= 1998|volume=37|pages=3518–3528|author=Khangulov, S. V.|display-authors=etal|pmid=9521673|issue=10}}</ref> [[Acetylene hydratase]] is an unusual [[metalloenzyme]] in that it catalyzes a hydration reaction. Two reaction mechanisms have been proposed, in one of which there is a direct interaction between the tungsten atom and the C≡C triple bond.<ref>{{cite book|first1=Felix |last1= ten Brink|editor=Peter M.H. Kroneck|editor2=Martha E. Sosa Torres
|title=The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment|series=Metal Ions in Life Sciences|volume=14|date=2014|publisher=Springer|chapter=Chapter 2. ''Living on acetylene. A Primordial Energy Source'' |pages=15–35|doi=10.1007/978-94-017-9269-1_2|pmid= 25416389|isbn= 978-94-017-9268-4}}
</ref> Although a tungsten-containing [[xanthine dehydrogenase]] from bacteria has been found to contain tungsten-molydopterin and also non-protein bound selenium, a tungsten-selenium molybdopterin complex has not been definitively described.<ref>{{cite journal|journal=Eur. J. Biochem. |date=1999|volume=264|issue=3|pages=862–71|title=Selenium-containing xanthine dehydrogenase from Eubacterium barkeri|doi=10.1046/j.1432-1327.1999.00678.x|author=Schrader, Thomas|author2=Rienhofer, Annette|author3=Andreesen, Jan R.|pmid=10491134|doi-access=free}}</ref>

In soil, tungsten metal oxidizes to the [[tungstate]] anion. It can be selectively or non-selectively imported by some [[Prokaryote|prokaryotic organisms]] and may substitute for [[molybdenum|molybdate]] in certain [[enzyme]]s. Its effect on the action of these enzymes is in some cases inhibitory and in others positive.<ref>{{Cite journal
 | last1 = Andreesen | first1 = J. R.
 | last2 = Makdessi | first2 = K.
 | doi = 10.1196/annals.1419.003
 | title = Tungsten, the Surprisingly Positively Acting Heavy Metal Element for Prokaryotes
 | journal = Annals of the New York Academy of Sciences
 | volume = 1125
 | issue = 1
 | pages = 215–229
 | year = 2008
 | pmid = 18096847
|bibcode = 2008NYASA1125..215A | s2cid = 19459237
 }}</ref> The soil's chemistry determines how the tungsten polymerizes; [[alkaline]] soils cause monomeric tungstates; [[acidic]] soils cause polymeric tungstates.<ref>{{cite journal|url=http://pubs.acs.org/cen/science/87/8703sci2.html|journal=Chemical & Engineering News|date=19 January 2009|title=Unease over Tungsten|pages=63–65|author=Petkewich, Rachel A. |volume=87|issue=3|doi=10.1021/cen-v087n003.p063}}</ref>

[[Sodium tungstate]] and [[lead]] have been studied for their effect on [[earthworm]]s. Lead was found to be lethal at low levels and sodium tungstate was much less toxic, but the tungstate completely inhibited their [[Reproduction|reproductive ability]].<ref>{{cite journal| title = Tungsten effects on survival, growth, and reproduction in the earthworm, eisenia fetida| author = Inouye, L. S.| display-authors = etal | journal =Environmental Toxicology and Chemistry|date = 2006|volume = 25| issue =3| pages = 763–8| doi = 10.1897/04-578R.1| pmid = 16566161| s2cid = 38620368}}</ref>

Tungsten has been studied as a biological copper metabolic [[Receptor antagonist|antagonist]], in a role similar to the action of molybdenum. It has been found that {{ill|tetrathiotungstate|zh|硫代鎢酸鹽|display=1}} salts may be used as biological copper [[chelation]] chemicals, similar to the [[tetrathiomolybdate]]s.<ref>{{cite journal|title=Thiotungstate-copper interactions II. The effects of tetrathiotungstate on systemic copper metabolism in normal and copper-treated rats|author=McQuaid A|author2=Lamand M|author3=Mason J|journal= J Inorg Biochem|volume=53|issue=3|pages=205–18|date=1994|doi=10.1016/0162-0134(94)80005-7|pmid=8133256}}</ref>
<!--===Early epidemiologic association with cancer===
On 20 August 2002, officials representing the U.S.-based [[Centers for Disease Control and Prevention]] announced that [[urine]] tests on [[leukemia]] patient families and control group families in the [[Fallon, Nevada]] area had shown elevated levels of tungsten in the bodies of both groups.<ref>{{cite web
|url = https://www.cdc.gov/nceh/clusters/Fallon/study.htm
|publisher = Centers for Disease Control and Prevention
|title = Cross-Sectional Exposure Assessment of Environmental Contaminants in Churchill County, Nevada
|date = 2003-02-06
|access-date = 2008-05-09}}</ref> Sixteen recent cases of [[cancer]] in children were discovered in the Fallon area, which has now been identified as a [[cancer cluster]]; although the majority of the cancer victims are not longtime residents of Fallon. However, there is not enough data to support a link between tungsten and leukemia at this time.<ref name="MullenFrankX">{{cite news |url = http://www.familiesagainstcancer.org/?id=344|newspaper = Reno Gazette-Journal|last = Mullen|first = Frank X.|title = Mouse Study Findings key in Fallon Cancer Cases, Scientists Say|date = April 27, 2006|access-date = 2008-06-17}}</ref> -->

===In archaea===
Tungsten is essential for some archaea. The following tungsten-utilizing enzymes are known:
* [[Aldehyde ferredoxin oxidoreductase]] (AOR) in ''[[Thermococcus]]'' strain ES-1
* [[Formaldehyde]] ferredoxin oxidoreductase (FOR) in ''[[Thermococcus litoralis]]''
* [[Glyceraldehyde-3-phosphate ferredoxin oxidoreductase]] (GAPOR) in ''[[Pyrococcus furiosus]]''
A ''wtp'' system is known to selectively transport tungsten in archaea:
* WtpA is tungsten-binding protein of [[ABC transporter|ABC family of transporters]]
* WtpB is a [[permease]]
* WtpC is [[ATPase]]<ref>
{{cite book | title=Archaea: New Models for Prokaryotic Biology |editor=Paul Blum|date=1 April 2008|isbn = 978-1-904455-27-1|publisher=Caister Academic Press}}</ref>