Re: Iddo's test 4, questions 9 and 10

Iddo Friedberg (
Wed, 14 Feb 1996 14:08:51 +0200 (IST)

On Wed, 14 Feb 1996, Luis wrote:

> >The identification of your amino acid's beta carbon as R or S
> >is correct. The configuration of the naturally occurring isoleucine
> >is not "c" but "d", so in Iddo's test, the correct answer is "2",
> >that is "a and d".
> >
> >An easy way to remember this is to think th"R"eonine and i"S"oleucine!
> >
> Dear Gayle,
> thanks for the correct answers, especially for the nice trick to remember=20
> the natural enantiomers.
> I'm still wondering: is there any reason for this ?
> Luis

"Reason" in evolutionary terms is a chicken & egg questions. The most
obvious "reason" is that enzyme substrate recognition sites are sensitive to
chirality. So the "reason" that (most) life on earth is using R-beta-Threonine
and S-beta-isoleucine is that the enzymes dealing with these amino-acids
wont recognize their enantiomers. But was there any selective a-priori force
towards that particular stereospecifity? I've tried to start a discussion
regrding the L-alpha carbon - why was it chosen. Check out the replies I've
got in this archive. Common wisdom, is that they were randomly selected in
the primordial soup.

Just my 0.02$


Iddo Friedberg ("\''/").___..--''"`-._
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