Deiodinase


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

Types

Types of deiodinases include:
familyprosthetic groupgenes
Iodothyronine deiodinaseDIO1, DIO2, DIO3
Iodotyrosine deiodinaseFlavin mononucleotide IYD

Iodothyronine deiodinases catalyze release of iodine directly from the thyronine hormones. They are selenocysteine-dependent membrane proteins with a catalytic domain resembling Peroxiredoxins. Three related isoforms, deiodinase type I, II, and III, contribute to activation and inactivation of the initially released hormone precursor T4 into T3 or rT3 in target cells. The enzymes catalyze a reductive elimination of iodine, 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.

Starvation response

In starvation, deiodinase 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. This is achieved by the latter organs expressing deiodinase II rather than Deiodinase I as in most peripheral tissues.

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.