3,5-Diiodothyronine (3,5-T₂) is an active

thyroid hormone File:Thyroid_system.svg, upright=1.5, The thyroid system of the thyroid hormones triiodothyronine, T3 and T4 rect 376 268 820 433 Thyroid-stimulating hormone rect 411 200 849 266 Thyrotropin-releasing hormone rect 297 168 502 200 Hypothalamus r ...

within the class of iodothyronines. It has two

iodine Iodine is a chemical element; it has symbol I and atomic number 53. The heaviest of the stable halogens, it exists at standard conditions as a semi-lustrous, non-metallic solid that melts to form a deep violet liquid at , and boils to a vi ...

atoms at positions 3 and 5 of its inner ring.

Biological effects

3,5-T₂ is an active thyroid hormone. It stimulates the TR-beta receptor for thyroid hormones and thus increases energy expenditure. It has agonistic (thyromimetic) effects at

myocardial Cardiac muscle (also called heart muscle or myocardium) is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. It is an involuntary, striated muscle that constitutes the main tissue of the wall of ...

tissue and

pituitary The pituitary gland or hypophysis is an endocrine gland in vertebrates. In humans, the pituitary gland is located at the base of the brain, protruding off the bottom of the hypothalamus. The pituitary gland and the hypothalamus control much of th ...

, which results in 3,5-T₂ suppressing TSH release. 3,5-T₂ is an

allosteric In the fields of biochemistry and pharmacology an allosteric regulator (or allosteric modulator) is a substance that binds to a site on an enzyme or receptor distinct from the active site, resulting in a conformational change that alters the p ...

regulator of the

cytochrome c oxidase The enzyme cytochrome c oxidase or Complex IV (was , now reclassified as a translocasEC 7.1.1.9 is a large transmembrane protein complex found in bacteria, archaea, and the mitochondria of eukaryotes. It is the last enzyme in the Cellular respir ...

, the complex IV of the

electron transport chain An electron transport chain (ETC) is a series of protein complexes and other molecules which transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples th ...

. It increases its activity by preventing the interaction of

adenosine triphosphate Adenosine triphosphate (ATP) is a nucleoside triphosphate that provides energy to drive and support many processes in living cell (biology), cells, such as muscle contraction, nerve impulse propagation, and chemical synthesis. Found in all known ...

(ATP) as an allosteric inhibitor.

Clinical significance

In nonthyroidal illness syndrome 3,5-T₂ concentrations are increased. This could explain why patients with low T3 syndrome don't benefit from substitution therapy with thyroid hormones.

References

External links

* {{DEFAULTSORT:Diiodothyronine, 3, 5- Iodinated tyrosine derivatives Human hormones Hormones of the hypothalamus-pituitary-thyroid axis Hormones of the thyroid gland