CompuServe Thread

>>My encyclopedia tells me there are a grand total of just over a hundred amino acids known, of which 22 are common and the rest are rare. Most of the rare ones occur in plants. Not all organisms use the same 20 aminos.<< WHAT?? I think they do (if you don't count the bacterial N- methyl-methionine). If they didn't, you get a heck of a bellyache, or at least a case of malnutrition, if you ate plants that used some weird amino in place of one of the 8 aminos you cannot make. Vegetarian animals eating certain plants could not survive at all if the biochemistry weren't essentially the same. Sure, there are other aminos than the standard ones in plants (and for that matter in animals– see the urea cycle for some of the same ones), but these extras are not incorporated into proteins during synthesis, as part of translation. For that, you need the 20 standards. Any others are either post-translational modifications, or else they are used for other things than building proteins, and you never see them in proteins (like citrulline and ornithine, etc). I'd be very surprised if (for example) bean sprouts directly incorporate canavanine into proteins in place of arginine during translation, although I don't know for sure where the stuff occurs in sprouts. It is poisonous, though– one of the few cases of weird plant amino acid poisoning known….