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thyroxine 5'-deiodinase
EC number1.97.1.10
CAS number70712-46-8
IntEnzIntEnz view
ExPASyNiceZyme view
MetaCycmetabolic pathway
PDB structuresRCSB PDB PDBe PDBsum
Gene OntologyAmiGO / QuickGO

Deiodinase (or "Monodeiodinase") is a peroxidase enzyme that is involved in the activation or deactivation of thyroid hormones.


Types of deiodinases include:

family prosthetic group genes
Iodothyronine deiodinase DIO1, DIO2, DIO3
Iodotyrosine deiodinase Flavin mononucleotide (FMN) IYD

Iodothyronine deiodinases catalyze release of iodine directly from the thyronine hormones. They are selenocysteine-dependent membrane proteins with a catalytic domain resembling Peroxiredoxins (Prx).[1] Three related isoforms, deiodinase type I, II, and III, contribute to activation and inactivation of the initially released hormone precursor T4 (thyroxine) into T3 (triiodothyronine) or rT3 (reverse triiodothyronine) in target cells. The enzymes catalyze a reductive elimination of iodine (the different isoforms attack different thyronine positions), thereby oxidizing themselves similar to Prx, followed by a reductive recycling of the enzyme.

Iodotyrosine deiodinase contributes to breakdown of thyroid hormones. It releases iodine, for renewed use, from iodinated tyrosines resulting from catabolism of iodothyronines. Iodotyrosine deiodinase employs a flavin mononucleotide cofactor and belongs to the NADH oxidase/flavin reductase superfamily.[2]

Starvation response[edit]

In starvation, deiodinase (specifically Deiodinase I) is inhibited thus lowering basal metabolic rate. However, in the brain, heart, skeletal muscle and thyroid, this is not so, as these organs must maintain homeostasis (skeletal muscle through shivering can increase temperature). This is achieved by the latter organs expressing deiodinase II rather than Deiodinase I as in most peripheral tissues.[citation needed]


Selenium in iodothyronine deiodinase, as selenocysteine, plays a crucial role in determining the free circulating levels of T3. Selenium deficiency can have implications in fall of T3 levels.


  1. ^ Schweizer U, Schlicker C, Braun D, Köhrle J, Steegborn C (July 2014). "Crystal structure of mammalian selenocysteine-dependent iodothyronine deiodinase suggests a peroxiredoxin-like catalytic mechanism". Proceedings of the National Academy of Sciences of the United States of America. 111 (29): 10526–31. doi:10.1073/pnas.1323873111. PMC 4115520. PMID 25002520.
  2. ^ Thomas SR, McTamney PM, Adler JM, Laronde-Leblanc N, Rokita SE (July 2009). "Crystal structure of iodotyrosine deiodinase, a novel flavoprotein responsible for iodide salvage in thyroid glands". The Journal of Biological Chemistry. 284 (29): 19659–67. doi:10.1074/jbc.M109.013458. PMC 2740591. PMID 19436071.

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