Thyroxine (BioDeep_00000001625)

描述信息

Thyroxine (3,5,3′,5′-tetraiodothyronine) or T4 is one of two major hormones derived from the thyroid gland, the other being triiodothyronine (T3). The major form of thyroid hormone in the blood is thyroxine (T4), which has a longer half-life than T3. In humans, the ratio of T4 to T3 released into the blood is approximately 14:1. T4 is converted to the active T3 (three to four times more potent than T4) within cells by enzymes known as deiodinases (5′-iodinase). Thyroxine is synthesized via the iodination of tyrosines (monoiodotyrosine) and the coupling of iodotyrosines (diiodotyrosine) in the thyroglobulin. Iodine is critical to the synthesis of thyroxine and other thyroid hormones. Through a reaction with the enzyme thyroperoxidase, iodine is covalently bound to tyrosine residues found in the thyroglobulin protein, forming monoiodotyrosine (MIT) and diiodotyrosine (DIT). Linking two moieties of DIT produces thyroxine. Combining one molecule of MIT and one molecule of DIT produces triiodothyronine. Thyroxine is released from thyroglobulin by proteolysis and secreted into the blood. Iodide is actively absorbed from the bloodstream and concentrated in the thyroid follicles where thyroxine is produced. If there is a deficiency of dietary iodine, the thyroid enlarges in an attempt to trap more iodine, resulting in a condition called goitre. More specifically, the lack of thyroid hormones will lead to decreased negative feedback on the pituitary gland, leading to increased production of thyroid-stimulating hormone, which causes the thyroid to enlarge, leading to goitre. Thyroxine can be peripherally de-iodinated to form triiodothyronine which exerts a broad spectrum of stimulatory effects on cell metabolism. Thyroid hormones function via a well-studied set of nuclear receptors, termed the thyroid hormone receptors. They act on nearly every cell in the body. In particular, thyroid hormones act to increase the basal metabolic rate, affect protein synthesis, help regulate long bone growth (synergy with growth hormone) and neural maturation, and increase the bodys sensitivity to catecholamines (such as adrenaline) by permissiveness. The thyroid hormones are essential to proper development and differentiation of all cells of the human body. These hormones also regulate protein, fat, and carbohydrate metabolism, affecting how human cells use energetic compounds. They also stimulate vitamin metabolism. Numerous physiological and pathological stimuli influence thyroid hormone synthesis. Levothyroxine, a manufactured form of thyroxine, was the most prescribed medication in the United States with more than 114 million prescriptions.

Thyroxine, one of the two major hormones secreted by the thyroid gland (the other is triiodothyronine). Thyroxine’s principal function is to stimulate the consumption of oxygen and thus the metabolism of all cells and tissues in the body. Thyroxine is formed by the molecular addition of iodine to the amino acid tyrosine while the latter is bound to the protein thyroglobulin. Excessive secretion of thyroxine in the body is known as hyperthyroidism, and the deficient secretion of it is called hypothyroidism.

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.[2] 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.[3]

The major form of thyroid hormone in the blood is thyroxine (T4), whose half-life of around one week[4] is longer than that of T3.[5] In humans, the ratio of T4 to T3 released into the blood is approximately 14:1.[6] T4 is converted to the active T3 (three to four times more potent than T4) within cells by deiodinases (5′-deiodinase). These are further processed by decarboxylation and deiodination to produce iodothyronamine (T1a) and thyronamine (T0a). All three isoforms of the deiodinases are selenium-containing enzymes, thus dietary selenium is essential for T3 production.

The thyroid hormone is one of the factors responsible for the modulation of energy expenditure. This is achieved through several mechanisms, such as mitochondrial biogenesis, adaptive thermogenesis, etc.[7]

American chemist Edward Calvin Kendall was responsible for the isolation of thyroxine in 1915.[8] In 2020, levothyroxine, a manufactured form of thyroxine, was the second most commonly prescribed medication in the United States, with more than 98 million prescriptions.[9][10] Levothyroxine is on the World Health Organization's List of Essential Medicines.[11]

(-)-Thyroxine. CAS Common Chemistry. CAS, a division of the American Chemical Society, n.d. https://commonchemistry.cas.org/detail?cas_rn=7488-70-2 (retrieved 2024-06-28) (CAS RN: 51-48-9). Licensed under the Attribution-Noncommercial 4.0 International License (CC BY-NC 4.0).
D-Thyroxine (D-T4) is a thyroid hormone that can inhibit TSH secretion. D-Thyroxine can be used for the research of hypercholesterolemia[1][2].
L-Thyroxine (Levothyroxine; T4) is a synthetic hormone for the research of hypothyroidism. DIO enzymes convert biologically active thyroid hormone (Triiodothyronine,T3) from L-Thyroxine (T4)[1].

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