CLINICAL MEDICINE

Detailed explanation-1: -Type III 5-Deiodinase Inactivates Thyroid Hormones 5-DIII is responsible for the majority of rT3 formation and T3 degradation and is considered the main thyroid hormone-inactivating enzyme. Expression of 5-DIII occurs in several tissues and cells that do not respond to thyroid hormone action.

Detailed explanation-2: -D3 activity in the normal uteroplacental unit regulates the transfer of maternal thyroid hormone to the fetus and, in patients with consumptive hypothyroidism, the rapid destruction of circulating thyroid hormone by tumoral D3 can produce severe hypothyroxinemia.

Detailed explanation-3: -Iodothyronine deiodinases (D1, D2, and D3) comprise a family of selenoproteins that are involved in the conversion of thyroxine (T(4)) to active triiodothyronine (T(3)), and also the inactivation of both thyroid hormones.

Detailed explanation-4: -Thyroid hormones are metabolized by different pathways: glucuronidation, sulfation, and deiodination, the latter being the most important. Three enzymes catalyzing deiodination have been identified, called type 1 (D1), type 2 (D2) and type 3 (D3) iodothyronine deiodinases.