5′-deiodinase
5′-deiodinases are iodothyronine deiodinases that convert the thyroid hormone thyroxine (T4) into triiodothyronine (T3). They play a crucial role in the activation of iodothyronines . Deiodinases are selenium-dependent enzymes .
Mechanism of activation
Deiodinases activate iodothyronines by removing an iodine atom on the outer ring (5′-position). In this way, T4 is converted to T3. Similar reactions mediated by 5'-deiodinases are the conversion of T3 to 3,5-T2 or of rT3 to 3,3'-T2 .
Types
Most vertebrates have two 5'-deiodinases that activate thyroid hormones. There is also an inactivating 5-deiodinase (type 3 deiodinase, D3).
Type | localization | function |
Type 1 (D1) | including liver and kidney | Deiodination of both rings (5-deiodination and 5′-deiodination) |
Type 2 (D2) | Heart muscle , skeletal muscle , central nervous system , adipose tissue , thyroid , pituitary gland | Outer ring deiodization (5′-deiodization) |
Type 3 (D3) | Fetal tissue and placenta | Inner ring deiodization (5-deiodization) |
Pathophysiology
Deiodinases are plastic enzymes that can be regulated by a variety of control influences. In severe general diseases, the 5′-deiodinase activity is reduced, while the activity of 5-deiodinase is increased ( non-thyroidal illness syndrome ).
Measurement of enzyme activity
In vitro , e.g. B. in cell culture experiments , the enzyme activity can be investigated by measuring the T3 formation or the iodine release under maximum substrate saturation with T4 and the required cosubstrates . In vivo , the activation of thyroid hormones can be estimated from equilibrium values of T4 and T3 with the help of the T3-T4 quotient or the calculated total activity of peripheral deiodinases (G D ).
literature
- ↑ B. Gereben, AM Zavacki, S. Ribich, BW Kim, SA Huang, WS Simonides, A. Zeöld, AC Bianco: Cellular and molecular basis of deiodinase-regulated thyroid hormone signaling. In: Endocr Rev . 29 (7), Dec 2008, pp. 898-938. doi: 10.1210 / er.2008-0019 . PMID 18815314 .
- ^ National Academy of Hypothyroidism , Deiodinases.