User:Boghog/Sandbox10
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| Names | |
|---|---|
| Other names
O-(4-hydroxy-3,5-diiodophenyl)-3,5-diiodo-L-tyrosine, (-)-thyroxine, 3,3′,5,5′-tetraiodo-L-thyronine
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| Identifiers | |
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| Properties | |
| C15H11I4NO4 | |
| Molar mass | 776.874 g·mol−1 |
| Appearance | white 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).
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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, serving as a reservoir for 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] With a half-life of approximately one week, thyroxine 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
[edit]
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 molecules, 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][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]
References
[edit]- ^ 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.
- ^ 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.
- ^ 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.
- ^ a b c d e f g 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.
- ^ a b c 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). doi:10.3390/nu13124469. PMC 8709459. PMID 34960019.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ a b c d Shahid MA, Ashraf MA, Sharma S (June 2023). "Physiology, Thyroid Hormone". StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing.