Why only L amino acids?

[Matthias Dreyer]

In article <00981067.D5F37D80 at vms.csd.mu.edu>, 6566friedman at vms.csd.mu.edu writes:
|> Does anyone have a plausible hypothesis to explain why only L amino 
|> acids are used in proteins?  I am teaching an introductory course in 
|> biochemistry this summer and this question was raised by a student.  
|> Please send your answers to:
|> 
 

Schulz & Schirmer (Prinicples of Protein Structure,1985)  dropped a few 
lines about this problem:

"... Although it had been shown that the intrinsic asymmetric beta-decay 
expresses itself as molecular asymmetry by preferentially destroying
D-amino acids, the observed effect of a few percent is too small to explain
the selection. Presumably it occured by chance and not because of a
slightly higher amino acid concentration that the L-system developed first.
Being farther advanced it then suppressed the emergence of a D-system.
Alternatively, both systems developed in parallel , and the L-system won
the ensuing competition by favorable environmental fluctuations, the impact
of which presumably far exceeded the impact of a few percent difference in
amino acid concentrations."

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Matthias Dreyer                            
Institut fuer Org. Chemie und Biochemie    
Universitaet Freiburg                      
Alberstr. 21                               
D- 79104 Freiburg                          
Germany                                    
e-mail: dreyer at bio5.chemie.uni-freiburg.de 
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