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Homocysteine thiolactone (HTL) is an organosulfur compound with the formula H 2 NCHC(O)SCH 2 CH 2. It is the thiolactone (intramolecular thioester ) of homocysteine . It is produced by methionyl-tRNA synthetase in an error-editing reaction that prevents translational incorporation of homocysteine into proteins .
Homocysteine can cyclize to give homocysteine thiolactone, a five-membered heterocycle. Because of this "self-looping" reaction, homocysteine-containing peptides tend to cleave themselves by reactions generating oxidative stress. [12] Homocysteine also acts as an allosteric antagonist at Dopamine D 2 receptors. [13]
The activation of the drug clopidogrel (top left) gives a thiolactone, which ring-opens. [3] Thiolactones are intermediates in the activation of some drugs. [4] In nature, the most common thiolactone is homocysteine thiolactone. It is produced from homocysteine. It may play a role in protein damage. [5]
As a consequence of the biochemical reactions in which homocysteine is involved, deficiencies of vitamin B 6, folic acid (vitamin B 9), and vitamin B 12 can lead to high homocysteine levels. [2] Other possible causes of hyperhomocysteinemia include genetics, excessive methionine intake, and other diseases.
Reaction 5 is catalyzed by cystathionine beta-synthase while reaction 6 is catalyzed by cystathionine gamma-lyase. The required homocysteine is synthesized from methionine in reactions 1, 2, and 3. The transsulfuration pathway is a metabolic pathway involving the interconversion of cysteine and homocysteine through the intermediate cystathionine .
The reaction of quadricyclane with DEAD is a 2σ + 2σ + 2π cycloaddition that on water takes place within 10 minutes at room temperature with 82% yield. The same reaction in toluene takes 24 hours at 80 °C with 70% yield. An emulsion reaction in fluorinated cyclohexane takes 36 hours and the neat reaction takes even longer (48 hours).
[1] [2] Patients observe these symptoms and seek medical advice from healthcare professionals. Because most people are not diagnostically trained or knowledgeable, they typically describe their symptoms in layman's terms, rather than using specific medical terminology. This list is not exhaustive.
Signs and symptoms of psychogenic polydipsia include: [3] Excessive thirst and xerostomia, leading to overconsumption of water; Hyponatraemia, causing headache, muscular weakness, twitching, confusion, vomiting, irritability etc., although this is only seen in 20–30% of cases.