BARBARA W. LOW AND JOHN T. EDSALL 



appear to satisfy the a and jS diffraction patterns, trans amide 

 groups are used exclusively. The second Pauling and Corey 

 requirement was that the identical chain residues should all be 



@>-s 



to 



Fig. 3. Fully extended trans polypeptide chain configuration 

 with chain residue bond lengths and bond angles. R. B. Corey 

 and L. Pauling, Proc. Roy. Soc. {London), B141, 10 (1953). 



Structurally equivalent and should make the maximum number 

 of strong intra- or m^^r-chain hydrogen bonds. When identical 

 chain residues are arranged so that one common operation 

 serves to translate the first residue position into the second, and 



396 



