Editing Iodothyronine deiodinase (section)

== Activation and inactivation ==

In tissues, deiodinases can either activate or inactivate thyroid hormones:
 
* ''Activation'' occurs by conversion of [[thyroxine]] (T<sub>4</sub>) to the active hormone [[triiodothyronine]] (T<sub>3</sub>) through the removal of an [[iodine]] atom on the outer ring.
* ''Inactivation'' of thyroid hormones occurs by removal of an [[iodine]] atom on the inner ring, which converts thyroxine to the inactive [[reverse triiodothyronine]] (rT<sub>3</sub>), or which converts the active [[triiodothyronine]] to [[diiodothyronine]] (T<sub>2</sub>).
The major part of [[thyroxine]] deiodination occurs within the cells.

Deiodinase 2 activity can be regulated by ubiquitination:
* The covalent attachment of [[ubiquitin]] inactivates D2 by disrupting dimerization and targets it to degradation in the [[proteosome]].<ref name="pmid18815314"/>
* Deubiquitination removing ubiquitin from D2 restores its activity and prevents proteosomal degradation.<ref name="pmid18815314">{{cite journal | vauthors = Gereben B, Zavacki AM, Ribich S, Kim BW, Huang SA, Simonides WS, Zeöld A, Bianco AC | display-authors = 6 | title = Cellular and molecular basis of deiodinase-regulated thyroid hormone signaling | journal = Endocrine Reviews | volume = 29 | issue = 7 | pages = 898–938 | date = December 2008 | pmid = 18815314 | pmc = 2647704 | doi = 10.1210/er.2008-0019 }}</ref>
* The Hedgehog cascade acts to increase D2 ubiquitination through [[WSB1]] activity, decreasing D2 activity.<ref name="pmid18815314"/><ref name="pmid15965468">{{cite journal | vauthors = Dentice M, Bandyopadhyay A, Gereben B, Callebaut I, Christoffolete MA, Kim BW, Nissim S, Mornon JP, Zavacki AM, Zeöld A, Capelo LP, Curcio-Morelli C, Ribeiro R, Harney JW, Tabin CJ, Bianco AC | display-authors = 6 | title = The Hedgehog-inducible ubiquitin ligase subunit WSB-1 modulates thyroid hormone activation and PTHrP secretion in the developing growth plate | journal = Nature Cell Biology | volume = 7 | issue = 7 | pages = 698–705 | date = July 2005 | pmid = 15965468 | pmc = 1761694 | doi = 10.1038/ncb1272 }}</ref>

D-propranolol inhibits thyroxine deiodinase, thereby blocking the conversion of T<sub>4</sub> to T<sub>3</sub>, providing some though minimal therapeutic effect.{{citation needed|date=May 2014}}