Thyroxine

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Thyroxine
Thyroxine2.svg
Names
Other names
O-(4-hydroxy-3,5-diiodophenyl)-3,5-diiodo-L-tyrosine, (-)-thyroxine, 3,3′,5,5′-tetraiodo-L-thyronine
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
EC Number
  • 206-088-9
PubChem CID
UNII
  • InChI=1S/C15H11I4NO4/c16-8-4-7(5-9(17)13(8)21)24-14-10(18)1-6(2-11(14)19)3-12(20)15(22)23/h1-2,4-5,12,21H,3,20H2,(H,22,23)
    Key: XUIIKFGFIJCVMT-UHFFFAOYSA-N
  • C1=C(C=C(C(=C1I)OC2=CC(=C(C(=C2)I)O)I)I)CC(C(=O)O)N
Properties
C15H11I4NO4
Molar mass 776.874 g·mol−1
Appearancewhite solid
Melting point 235-236
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Thyroxine, also known as T4, is a hormone produced by the thyroid gland. It is the primary form of thyroid hormone found in the blood and acts as a prohormone of the more active thyroid hormone, triiodothyronine (T3). [1] Thyroxine and its active metabolites are essential for regulating metabolic rate, supporting heart and muscle function, promoting brain development, and maintaining bone health. [2] [3]

Regulation

Thyroxine has a half-life of approximately one week and hence maintains relatively stable blood levels. Its production and release are controlled through a complex feedback loop involving the hypothalamus, pituitary gland, and thyroid gland. This regulatory system ensures that optimal hormone levels are maintained. [4]

Biosynthesis

Biosynthesis of thyroxine Thyroxine biosynthesis.svg
Biosynthesis of thyroxine

Thyroxine biosynthesis is a multi-step process that occurs in follicular cell within the thyroid gland. The synthesis of thyroxine requires adequate iodine supply and appropriate hormonal control. [5] [6] [4]

The process begins with the active uptake of iodide from the bloodstream by thyroid follicular cells through the sodium/iodide symporter (NIS) located in the basolateral membrane. Once inside the cell, iodide is transported to the follicular lumen, where it undergoes oxidation by the enzyme thyroid peroxidase (TPO) in the presence of hydrogen peroxide generated by the NADPH oxidase DUOX2. [6] The oxidized iodine then iodinates tyrosyl residues of thyroglobulin (Tg), a glycoprotein synthesized by thyroid cells and stored in the follicular lumen. [5] This process, known as organification, results in the formation of monoiodotyrosine (MIT) and diiodotyrosine (DIT) residues within the Tg molecule. [6] [4]

The final step in thyroxine synthesis involves the free radical mediated coupling of two DIT residues, catalyzed by TPO, to form T4 while still attached to the Tg backbone. [5] [6] When thyroid hormone is needed, Tg is internalized by thyrocytes, and proteolytic enzymes in lysosomes cleave the T4 from Tg, allowing for its release into the bloodstream. [4] This intricate biosynthetic pathway is tightly regulated by thyroid-stimulating hormone (TSH) from the pituitary gland, which influences virtually every stage of thyroid hormone production. [4]

Related Research Articles

<span class="mw-page-title-main">Endocrine system</span> Hormone-producing glands of a body

The endocrine system is a messenger system in an organism comprising feedback loops of hormones that are released by internal glands directly into the circulatory system and that target and regulate distant organs. In vertebrates, the hypothalamus is the neural control center for all endocrine systems.

<span class="mw-page-title-main">Thyroid</span> Endocrine gland in the neck

The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans, it is a butterfly-shaped gland located in the neck below the Adam's apple. It consists of two connected lobes. The lower two thirds of the lobes are connected by a thin band of tissue called the isthmus. Microscopically, the functional unit of the thyroid gland is the spherical thyroid follicle, lined with follicular cells (thyrocytes), and occasional parafollicular cells that surround a lumen containing colloid.

<span class="mw-page-title-main">Hypothyroidism</span> Insufficient production of thyroid hormones by the thyroid gland

Hypothyroidism is a disorder of the endocrine system in which the thyroid gland does not produce enough thyroid hormones. It can cause a number of symptoms, such as poor ability to tolerate cold, extreme fatigue, muscle aches, constipation, slow heart rate, depression, and weight gain. Occasionally there may be swelling of the front part of the neck due to goiter. Untreated cases of hypothyroidism during pregnancy can lead to delays in growth and intellectual development in the baby or congenital iodine deficiency syndrome.

<span class="mw-page-title-main">Iodothyronine deiodinase</span> Class of enzymes

Iodothyronine deiodinases (EC 1.21.99.4 and EC 1.21.99.3) are a subfamily of deiodinase enzymes important in the activation and deactivation of thyroid hormones. Thyroxine (T4), the precursor of 3,5,3'-triiodothyronine (T3) is transformed into T3 by deiodinase activity. T3, through binding a nuclear thyroid hormone receptor, influences the expression of genes in practically every vertebrate cell. Iodothyronine deiodinases are unusual in that these enzymes contain selenium, in the form of an otherwise rare amino acid selenocysteine.

Thyroid-stimulating hormone (also known as thyrotropin, thyrotropic hormone, or abbreviated TSH) is a pituitary hormone that stimulates the thyroid gland to produce thyroxine (T4), and then triiodothyronine (T3) which stimulates the metabolism of almost every tissue in the body. It is a glycoprotein hormone produced by thyrotrope cells in the anterior pituitary gland, which regulates the endocrine function of the thyroid.

<span class="mw-page-title-main">Triiodothyronine</span> Chemical compound

Triiodothyronine, also known as T3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate.

<span class="mw-page-title-main">Thyroglobulin</span> Protein produced and used by the thyroid

Thyroglobulin (Tg) is a 660 kDa, dimeric glycoprotein produced by the follicular cells of the thyroid and used entirely within the thyroid gland. Tg is secreted and accumulated at hundreds of grams per litre in the extracellular compartment of the thyroid follicles, accounting for approximately half of the protein content of the thyroid gland. Human TG (hTG) is a homodimer of subunits each containing 2768 amino acids as synthesized.

<span class="mw-page-title-main">Thyroid follicular cell</span> Hormone-producing cell in the thyroid gland

Thyroid follicular cells (also called thyroid epithelial cells or thyrocytes) are the major cell type in the thyroid gland, and are responsible for the production and secretion of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). They form the single layer of cuboidal epithelium that makes up the outer structure of the almost spherical thyroid follicle.

<span class="mw-page-title-main">Propylthiouracil</span> Medication used to treat hyperthyroidism

Propylthiouracil (PTU) is a medication used to treat hyperthyroidism. This includes hyperthyroidism due to Graves' disease and toxic multinodular goiter. In a thyrotoxic crisis it is generally more effective than methimazole. Otherwise it is typically only used when methimazole, surgery, and radioactive iodine is not possible. It is taken by mouth.

<span class="mw-page-title-main">Wolff–Chaikoff effect</span> Effect of iodine on the thyroid

The Wolff–Chaikoff effect is a presumed reduction in thyroid hormone levels caused by ingestion of a large amount of iodine.

<span class="mw-page-title-main">Thyroid peroxidase</span> Enzyme expressed mainly in the thyroid gland

Thyroid peroxidase, also called thyroperoxidase (TPO), thyroid specific peroxidase or iodide peroxidase, is an enzyme expressed mainly in the thyroid where it is secreted into colloid. Thyroid peroxidase oxidizes iodide ions to form iodine atoms for addition onto tyrosine residues on thyroglobulin for the production of thyroxine (T4) or triiodothyronine (T3), the thyroid hormones. In humans, thyroperoxidase is encoded by the TPO gene.

<span class="mw-page-title-main">Thyroid disease</span> Medical condition

Thyroid disease is a medical condition that affects the function of the thyroid gland. The thyroid gland is located at the front of the neck and produces thyroid hormones that travel through the blood to help regulate many other organs, meaning that it is an endocrine organ. These hormones normally act in the body to regulate energy use, infant development, and childhood development.

<span class="mw-page-title-main">Reverse triiodothyronine</span> Chemical compound

Reverse triiodothyronine, also known as rT3, is an isomer of triiodothyronine (T3).

An antithyroid agent is a hormone inhibitor acting upon thyroid hormones.

<span class="mw-page-title-main">Sodium/iodide cotransporter</span> Mammalian protein found in Homo sapiens

The sodium/iodide cotransporter, also known as the sodium/iodide symporter (NIS), is a protein that in humans is encoded by the SLC5A5 gene. It is a transmembrane glycoprotein with a molecular weight of 87 kDa and 13 transmembrane domains, which transports two sodium cations (Na+) for each iodide anion (I−) into the cell. NIS mediated uptake of iodide into follicular cells of the thyroid gland is the first step in the synthesis of thyroid hormone.

<span class="mw-page-title-main">Thyroid hormones</span> Hormones produced by the thyroid gland

Thyroid hormones are any hormones produced and released by the thyroid gland, namely triiodothyronine (T3) and thyroxine (T4). They are tyrosine-based hormones that are primarily responsible for regulation of metabolism. T3 and T4 are partially composed of iodine, derived from food. A deficiency of iodine leads to decreased production of T3 and T4, enlarges the thyroid tissue and will cause the disease known as simple goitre.

<span class="mw-page-title-main">Iopanoic acid</span> Chemical compound

Iopanoic acid is an iodine-containing radiocontrast medium used in cholecystography. Both iopanoic acid and ipodate sodium are potent inhibitors of thyroid hormone release from thyroid gland, as well as of peripheral conversion of thyroxine (T4) to triiodothyronine (T3). These compounds inhibit 5'deiodinase (5'DID-1 and 5'DID-2) enzymes, which catalyse T4-T3 conversion in the thyroid cell, liver, kidney, skeletal muscle, heart, brain, pituitary. This accounts for the dramatic improvement in both subjective and objective symptoms of hyperthyroidism, particularly when they are used as an adjunctive therapy with thioamides (propylthiouracil, carbimazole). They can be used in the treatment of patients with severe thyrotoxicosis (thyroid storm) and significant morbidity (e.g., myocardial infarction, or stroke) for rapid control of elevated plasma triiodothyronine concentrations. The use of iopanoic acid for treatment of thyrotoxicosis has been discontinued in the United States.

<span class="mw-page-title-main">Iodotyrosine deiodinase</span> Protein-coding gene in the species Homo sapiens

Iodotyrosine deiodinase, also known as iodotyrosine dehalogenase 1, is a type of deiodinase enzyme that scavenges iodide by removing it from iodinated tyrosine residues in the thyroid gland. These iodinated tyrosines are produced during thyroid hormone biosynthesis. The iodide that is scavenged by iodotyrosine deiodinase is necessary to again synthesize the thyroid hormones. After synthesis, the thyroid hormones circulate through the body to regulate metabolic rate, protein expression, and body temperature. Iodotyrosine deiodinase is thus necessary to keep levels of both iodide and thyroid hormones in balance.

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

<span class="mw-page-title-main">Iodine in biology</span> Use of Iodine by organisms

Iodine is an essential trace element in biological systems. It has the distinction of being the heaviest element commonly needed by living organisms as well as the second-heaviest known to be used by any form of life. It is a component of biochemical pathways in organisms from all biological kingdoms, suggesting its fundamental significance throughout the evolutionary history of life.

References

  1. ↑ Li J, Bai L, Wei F, Wei M, Xiao Y, Yan W, et al. (2020). "Effect of Addition of Thyroxine in the Treatment of Graves' Disease: A Systematic Review". Frontiers in Endocrinology. 11: 560157. doi: 10.3389/fendo.2020.560157 . PMC   7868565 . PMID   33569041.
  2. ↑ Kim HY, Mohan S (June 2013). "Role and Mechanisms of Actions of Thyroid Hormone on the Skeletal Development". Bone Research. 1 (2): 146–161. doi:10.4248/BR201302004. PMC   4472099 . PMID   26273499.
  3. ↑ Mullur R, Liu YY, Brent GA (April 2014). "Thyroid hormone regulation of metabolism". Physiological Reviews. 94 (2): 355–82. doi:10.1152/physrev.00030.2013. PMC   4044302 . PMID   24692351.
  4. 1 2 3 4 5 6 Rousset B, Dupuy C, Miot F, Dumont J (September 2015). "Chapter 2 Thyroid Hormone Synthesis And Secretion". In Feingold KR, Anawalt B, Blackman MR, Boyce A, Chrousos G, Corpas E, et al. (eds.). Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc. PMID   25905405.
  5. 1 2 3 Sorrenti S, Baldini E, Pironi D, Lauro A, D'Orazi V, Tartaglia F, et al. (December 2021). "Iodine: Its Role in Thyroid Hormone Biosynthesis and Beyond". Nutrients. 13 (12): 4469. doi: 10.3390/nu13124469 . PMC   8709459 . PMID   34960019.
  6. 1 2 3 4 Shahid MA, Ashraf MA, Sharma S (June 2023). "Physiology, Thyroid Hormone". StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. PMID   29763182.
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