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why only L-amino acids?

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why only L-amino acids?

Postby Nite » Sat Aug 20, 2005 4:46 pm

Hi all!!

I have a few questions here. hope somebody can help to clear it:D.

1. Why natural occuring proteins contain mostly of L-amino acids, while those that are synthesised in the lab consist of 50% L and 50% D? Is there a special functions of L-amino acids?

2. What test is carried out to check if an amino acid is D or L?

3. Is D and L configuration "switchable"??


Cheerzz


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Postby Chris4 » Sat Aug 20, 2005 8:47 pm

You mean why don't they contain a racemic mixture (mixture of L and D isomers).
1) Although no one knows the exist answer it appears that L - amino acids are slightly more stable. Also amino acids from the solar system, metorites etc, are all L amino acids so maybe thats why all amino acids on earth are L-.
Maybe these will help:
http://web99.arc.nasa.gov/~astrochm/aachiral.html
http://www-biol.paisley.ac.uk/courses/s ... ality.html
http://www.ast.cam.ac.uk/AAO/local/www/ ... ality.html

2) Planes of symmetry tests. I did these a couple of years ago using a polarimeter. Check out the animation on a polarimeter here
http://cwx.prenhall.com/petrucci/medial ... io/28.html

3) I haven't come across switchable L and D-amino acids. You mean spontaneously? The polarimeter experiment wouldn't work if your solution of L-amino acids was rapidly switching between two confirmations.

All this chirality stuff reminded me of the Thalidomide tragedy in the 1950s and 60s. A drug given to pregnant women for morning sickness, but it was a racemic mixture and they didn't know that one enantiomer was teratogenic (causing physical defects during birth). So a lot of childen were born with birth defects. :(
http://en.wikipedia.org/wiki/Thalidomide

Hope all that helped :D
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Postby Nite » Tue Aug 23, 2005 4:29 pm

Thanks a lot for the info chris.\ :D. It's very useful.

Do you know what will happen if human consumed D amino acids?

Is D amino acids known to have detrimental effects on humans?
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Postby Daniel Tillett » Tue Aug 23, 2005 11:17 pm

From memory we have enzyme able to degrade D-amino acids. Also some natural peptides (small proteins) contain D-amino acids so like everything in nature every rule has an exception :)

Daniel

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