Function
Responsible for the deiodination of T4 (3,5,3',5'-tetraiodothyronine) into T3 (3,5,3'-triiodothyronine) and of T3 into T2 (3,3'-diiodothyronine). Is responsible for the majority of the intracellular T3 in tissues such as the pituitary, brain and brown fat by mediating local deiodination of T4, and is important in regulating thyroid hormone action in these tissues. Plays a major role in development.