PROTEINS 



559 



in a radial direction, than the inner side of the curl (Ohara, 1958^ 



1939)- 

 Alol^cular structure of keratin. Astbury (1935 c) has demonstrated 



that stretched hairs produce quite a different X-ray diagram from 



unstretched ones. The difference is especially evident when the 



\ 



NH 



CO' 



rf 



CO-' 



\ 



CHR 



CHR 



NH 



<o 



Co 

 >; 



<r> 



II 



I5 



NH 



CO 



C0-- 



CHR 



NH 

 fi- Keratin 



y CH.R)-C0-NH- 



NH 



I 

 CO 



■R':CH 



'■' I 

 NH 

 CO 



CH^ 



CH (R\-NH' CO-\R)CH ^ 

 NH 



CO 



. I 

 IR)CH 



NH 

 I 



^CH 



NH 



I 

 CO 



CH® 



'. ..■■' CO 



■,RyCO-NH-(§)CH'' 



a-Kerafin 



b) 



Fig. 171. a) ^-keratin (after Astbury, 1933c). h) Folding of the polypeptide chain; R side 



chains (after .'\stbury and Bell, 1941). 



elongation takes place in a vapour-saturated chamber at 100° C, where 

 about 100% elongation can be attained. The X-ray picture shows the 

 distance between the members of the chain to be 3.38 A. This tallies 

 well with the chain period of silk fibroin, viz. 3.5 A and it may 

 therefore be assumed that elongated primary valence chains of poly- 

 peptide thread molecules are also present in stretched wool. As the 

 fibre period in unstretched wool is 5 .06 A, some other modification, 

 which Astbury designates as a-keratin, must be involved. The keratin 

 in stretched wool is known as /5-keratin. By folding the polypeptide 

 chain, he derives a-keratin from jS-keratin, arguing that by the mutual 

 attraction of two NH and CO groups separated by five valence bonds, 

 pseudo-diketopiperazine rings are liable to be formed. Taking into 

 account the rules of distance, the fibre period of a-keratin for a chain 



