from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A sulfur-containing essential amino acid, C5H11NO2S, obtained from various proteins or prepared synthetically and used as a dietary supplement and in pharmaceuticals.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A sulphur-containing essential amino acid, C5H11NO2S, found in most protein; it is lipotropic.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a crystalline amino acid containing sulfur; found in most proteins and essential for nutrition
I also just learned that methionine is resistant to cytosine deamination, and it sets the reading frame.
In intro bio (which I took almost forty years ago) we were told that the reason that methionine is the universal "start" amino acid (among prokaryotes) is that it can be modified in such a way (by the addition of an aldehyde functional group, yielding N-formylmethionine) as to set the direction of polymerization by limiting the addition of new amino acids to one end of the growing polypeptide chain.
N-formyl-methionine is still used in the mitochondria (which is a direct descendant of prokaryotic symbiotes).
In the nucleus, unmodified methionine is used as the start residue.
Well no, I was asking people's opinions on why methionine is a nearly universal start codon.
It provides plenty of methionine, which is both a source of sulfur for the antioxidants in the mitochondria and a source of methyl groups for methylation of the fats in the cellular membrane thereby keeping them more fluid while at the same time more saturated.
If we have plenty of folate, vitamin B12, and vitamin B6 we can easily convert homocysteine into methionine, which is why doctors always recommend folic acid, vitamin B12 and vitamin B6 to treat elevated levels of homocysteine.
My doctoral thesis concerned what is today referred to as C1 metabolism, more specifically the conversion of formic acid, formaldehyde and methanol to the fully reduced state of methyl groups in methionine.
There is amino acid called methionine which yeast does not have.
Also known as "methyl donors," sulphur-producing amino acids assist in the formation of methionine, which is the first amino acid to "join the team" when creating many new cells and is, therefore, a "must have" to promote an effective use of protein.
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