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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 .
Total plasma homocysteine. Homocysteine levels typically are higher in men than women, and increase with age. [15] [16] Common levels in Western populations are 10 to 12 μmol/L, and levels of 20 μmol/L are found in populations with low B-vitamin intakes or in the elderly (e.g., Rotterdam, Framingham). [17] [18]
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.
The cold water can cause heart attack due to severe vasoconstriction, [2] where the heart has to work harder to pump the same volume of blood throughout the arteries. For people with pre-existing cardiovascular disease , the additional workload can result in myocardial infarction and/or acute heart failure , which ultimately may lead to a ...
If B 12 is absent, the forward reaction of homocysteine to methionine does not occur, homocysteine concentrations increase, and the replenishment of tetrahydrofolate stops. [139] Because B 12 and folate are involved in the metabolism of homocysteine, hyperhomocysteinuria is a non-specific marker of deficiency.
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.
Tea and toast syndrome is a form of malnutrition commonly experienced by elderly people who cannot prepare meals and tend to themselves. The term is not intrinsic to tea or bread products only; rather, it describes limited dietary patterns that lead to reduced calories resulting in a deficiency of vitamins and other nutrients.