from Wiktionary, Creative Commons Attribution/Share-Alike License.
- noun biochemistry A naturally-occurring
amino acid, present in several enzymes, whose structure is that of cysteinebut with the sulfuratom replaced by one of selenium
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So it will need to be consistent not with merely the ribosome and the bacterial flagella, but also the octopus's eye, the panda's thumb, and the jerry-rigged way that selenocysteine is kluged into the genetic code.
The awkward way in which selenocysteine is kluged into the genetic code (which is not unique to Tetrahymena; we do it too), sharing a termination codon instead of having one to itself seems like a good example of a molecular "panda's thumb," reflecting the inherent difficulty of a late addition to the frozen accident of the genetic code.
The third termination codon, UGA, does signal for termination, but can also be used in a context-dependent manner (depending on RNA structure) to code the amino acid, selenocysteine.
Although all forms of selenium described above are fairly well absorbed by the body, some studies show a slight edge to selenomethionine over selenocysteine, selenocysteine over sodium selenate, and sodium selenate over sodium selenite.
The most widely-available are selenomethionine and selenocysteine.
Instead, they possess a linked thioredoxin-glutathione system with a selenocysteine-containing enzyme thioredoxin glutathione reductase (TGR) as the single redox hub that controls the overall redox homeostasis.
Specific gene sets associated with the central metabolism of C. aurimucosum apparently provide enhanced metabolic flexibility and adaptability in aerobic, anaerobic and low-pH environments, including gene clusters for the uptake and degradation of aromatic amines, L-histidine and L-tartrate as well as a gene region for the formation of selenocysteine and its incorporation into formate dehydrogenase.
The European Food Safety Authority (EFSA) has said there is insufficient data to back the safety of the selemium form, Se-methyl-L-selenocysteine (Semethylselenocysteine), in food supplements.