Skip to main content

Table 2 General characteristics of the iodothyronine deiodinases [16]

From: Hypothyroidism and brain developmental players

Characteristic D1 D2 D3
Reaction kinetics Ping-pong Sequential Sequential
Reaction catalyzed (Deiodination) 5 or 5' (ORD+IRD) 5' (ORD) 5 (IRD)
Main form T4-T3, rT3- T2 - T4- rT3, T3- T2 - T4- rT3- T2
Substrate preference 5: T4S>T3S>>T3, T4 T4>rT3 T3>T4
5': rT3, rT3S>T2S>>T4
Sulfation of substrates Stimulation Inhibition Inhibition
Substrate limiting KM 0.5 mM 1–2 nM 5–20 mM
In vitro cofactor limiting KM 1–10 Mm DTT >10 mM DTT =70 mM DTT
Molecular mass (kDa) 29 30 32
Selenocysteine present present present
Homodimer Yes Yes Yes
Location - Liver, kidney, thyroid and pituitary. - Pituitary, brain, BAT, thyroida, hearta and skeletal musclea. - Brain, skin, uterus, placenta, fetus and in other sites of the maternal- fetal interface, such as the umbilical arteries and veins.
Subcellular location - Liver: endoplasmic reticulum. - kidney: basolateral plasma membrane - Microsomal membranes - Microsomal membranes
Functions - Production serum T3 and the clearance of serum rT3. - Catalyzes the outer ring deiodination of T4 to T3 and is thus important for the local production of T3. - Catalyzes the inner ring deiodination of T4 to rT3 and of T3 to 3,3'-T2.
Activity in hypothyroidism - Decrease in liver and kidney. - Increase in all tissues. - Decrease in brain.
- Increase in thyroid.
Low-T3 syndrome - Decrease - No change - No change
Active site residues - Selenocysteine histidine and phenylalanine. - (Seleno-)cysteine? - Selenocysteine
Human gene structure and location - 1p32-p33, 17.5 kb and 4 exons. - 14q24.3, 2 exons and 7.4-kb intron. - 14q32
Promoter elements - TRE, RXR, no CAAT or TATA box. -- --
Propylthiouracil inhibitor ++++ + +/-
Aurothioglucose inhibitor ++ ++
Iopanoic acid inhibitor +++ ++++ +++
Thiouracils ++++ -/+ -
Iodoacetate + ?
Flavonoids + +++ +++
  1. aHumans only. T2 is diiodothyronine, T3 is triiodothyronine, rT3 is reverse triiodothyronine, T4 is thyroxine, T2S is diiodothyronine sulfate, T3S is triiodothyronine sulfate, T4S is thyroxine sulfate, rT3S is reverse triiodothyronine sulfate, ORD is outer ring deiodination, IRD is inner ring deiodination, TRE is T3-responsive element, RXR is retinoid X receptors and DDT is dithiols.