Deiodinase

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deiodinase, iodothyronine, type I
Identifiers
Symbol	DIO1 TXDI1
HUGO	2883
Entrez	1733
OMIM	147892
RefSeq	NM_000792
UniProt	P49895
Other data
EC number	1.97.1.10
Locus	Chr. 1 p32-p33

deiodinase, iodothyronine, type II
Identifiers
Symbol	DIO2
HUGO	2884
Entrez	1734
OMIM	601413
RefSeq	NM_000793
UniProt	Q92813
Other data
Locus	Chr. 14 q24.2-24.3

deiodinase, iodothyronine, type III
Identifiers
Symbol	DIO3 TXDI3
HUGO	2885
Entrez	1735
OMIM	601038
RefSeq	NM_001362
UniProt	P55073
Other data
Locus	Chr. 14 q32

deiodinase, iodothyronine, type III opposite strand
Identifiers
Symbol	DIO3OS C14orf134
HUGO	20348
Entrez	64150
OMIM	608523
RefSeq	NM_022345
UniProt	Q9HAR6
Other data
Locus	Chr. 14 q32.33

Deiodinase (EC 1.97.1.10) is an enzyme important in the action of thyroid hormones.

Deiodinases are unusual in that the enzyme contains selenium, in the form of an otherwise rare amino acid selenocysteine.

Contents 1 Activation and inactivation 2 Types 3 Synthesis 4 External links

[edit] Activation and inactivation

In the tissues, deiodinases can either activate or inactivate thyroid hormones:

• Activation occurs by conversion of the prohormone thyroxine (T4) to the active hormone triiodothyronine (T3) through the removal of an iodine atom on the outer ring.
• Inactivation of thyroid hormones occurs by removal of an iodine atom on the inner ring which converts thyroxine to the inactive reverse triiodothyronine (rT3), or which converts the active triiodothyronine to the inactive diiodothyronine (T2). The major part of thyroxine deiodination occurs within the target cells.

[edit] Types

In most vertebrates, there are three types of enzymes that can deiodinate thyroid hormones:

Type	Location	Function
type I (DI)	is commonly found in the liver, kidney, muscle tissue and thyroid gland	DI can deiodinate both rings
type II deiodinase (DII)	mostly in the brain but also in the testis and thyroid	DII can only deiodinate the outer ring of the prohormone thyroxine (or the metabolically inactive reverse triiodothyronine) and is the major activating enzyme
type III deiodinase (DIII)	found in the fetal tissue and the placenta	DIII can only deiodinate the inner ring of thyroxine or triiodothyronine and is the major inactivating enzyme

[edit] Synthesis

[edit] External links

• MeSH Deiodinase