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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]
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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.
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Consequently, a thermochemical cycle with i steps can be defined as sequence of i reactions equivalent to water-splitting and satisfying equations (4), (5) and (10). The key point to remember in that case is that the process temperature T H can theoretically be arbitrary chosen (1000K as a reference in most of the past studies, for high ...
Since liquid water flows, ocean waters cycle and flow in currents around the world. Since water easily changes phase, it can be carried into the atmosphere as water vapour or frozen as an iceberg. It can then precipitate or melt to become liquid water again. All marine life is immersed in water, the matrix and womb of life itself. [7]