246 



KERATIN AND KERATINIZATION 



macromolecular level, that in fact it consists of two components : one of a 

 fibrous, relatively-crystalline character, the other less well-organized, and 

 containing the larger part of the cystine residues. 



This view was implicit in the earlier X-ray work (Astbury and Woods, 

 1933 ; Astbury, 1943) which showed clearly that the crystalline fraction of 

 keratin fibres, as judged by the persistence of the a-pattern, was unaltered 

 by a variety of chemical treatments which involved the disulphide bridges 

 and the acid and basic side chains of the protein. It was recognized that 



s-s- 



■s s 



[a] 



-S-S- 



-S-S- 



(b) 



Fig. 101. The classical view of the location of disulphide bonds (S 2 ) as 



cross-linkage between polypeptide chains. In (a) all the linkages are 



shown as side chains. In (b) the possibility of the linkage occurring in 



the main chain direction is indicated. 



most of these reactions must take place in the " non-crystalline " regions. 

 The size of the various reflections of the X-ray diagram and the greater 

 strength of reflections arising from planes parallel to the fibre axis showed 

 that the crystallites were small (< 100 A wide), long and thin with their 

 long axis parallel to the fibre axis. They may well be identical with the 

 filaments seen in electron micrographs. 



More direct, morphological evidence was later obtained by examining 

 fragments of disintegrated fibres. A system of filaments (microfibrils) 

 embedded in an amorphous matrix was proposed by Farrant, Rees and 



