The function of DIO2 (iodothyronine deiodinase 2, ENSG00000211448) is as follows. Plays a crucial role in the metabolism of thyroid hormones (TH) and has specific roles in TH activation and inactivation by deiodination (PubMed:12586771, PubMed:11108274, PubMed:10403186, PubMed:18821722). Catalyzes the deiodination of L-thyroxine (T4) to 3,5,3'-triiodothyronine (T3), 3,3',5'-triiodothyronine (rT3) to 3,3'- diiodothyronine (3,3'-T2) and 3',5'-diiodothyronine (3',5'-T2) to 3'- monoiodothyronine (3'-T1) via outer-ring deiodination (ORD) (PubMed:12586771, PubMed:11108274, PubMed:10403186, PubMed:18821722, PubMed:18339710). Catalyzes the phenolic ring deiodinations of 3,3',5'- triiodothyronamine and 3',5'- diiodothyronamine (PubMed:18339710). {ECO:0000269|PubMed:10403186, ECO:0000269|PubMed:11108274, ECO:0000269|PubMed:12586771, ECO:0000269|PubMed:18339710, ECO:0000269|PubMed:18821722}.