Iodothyronine deiodinase (<db_xref db="EC" dbkey="1.97.1.10"/>) (DI) [<cite idref="PUB00002931"/>] is the vertebrate enzyme responsible for the deiodination ofthe prohormone thyroxine (T4 or 3,5,3',5'-tetraiodothyronine) into the biologically active hormone T3(3,5,3'-triiodothyronine) and of T3 into the inactive metabolite T2 (3,3'-diiodothyronine). All known DI areproteins of about 250 residues that contain a selenocysteine at their active site. Three types of DI areknown, type II is essential for providing the brain with the appropriate levels of T3 during the criticalperiod of development, and type III is essential for the regulation of thyroid hormone inactivation duringembryological development. <p>This signature found in the central part of the enzyme, which contains the active site selenocysteine.</p> Iodothyronine deiodinase, active site