176 



KERATIN AND KERATINIZATION 



Leeds School, capable of co-ordinating a great deal of physicochemical 

 data. Recent discussions of the elastic properties of fibres are given by 

 Feughehnan (1959), Peters and Woods (1956), Skertchly and Woods 

 (1960). 



The conclusion that the a-keratin chain was half as long as the ^-chain 

 was not universally accepted and other models were also proposed. 

 Notably Ambrose and Hanby (1949) and Zahn (1947 and 1949) proposed 

 a fold, which yielded the required axial periodicities and gave an a -> /J 

 extensibility of ~ 33%. This appeared to accord with the observation that 

 the actual transformation of the a-crystallites into the jS-form took place 

 between fibre extensions of 20-45% (phase II, Fig. 70) which could be 



~Xfu%r 



.t*o Cl+J> cL^ji o m >s 



Fig. 72. The Astbury model for a-keratin: arrows represent the 

 direction of the main chain; $ represents a side chain pointing up from 

 the plane of the diagram ; O represents a side chain pointing down from 

 the plane of the diagram. From Astbury and Bell (1941). 



interpreted to mean that the crystallites themselves were fully extended by 

 a change of length from 1*2 to ~ 1*5, i.e. of the order of 25-30%. Ambrose 

 and Hanby also claimed that the less-folded structure fitted in better with 

 their observations on the average orientation of H-bonds inferred from 

 absorption spectra of polarized infra-red radiation (p. 197). Other pro- 

 posals stemmed from Huggins (1943). It is to be noted that none of these 

 earlier models appears capable of yielding an axial periodicity of 1-5 A 

 which is now recognized as being fundamental to the a-structure (p. 182). 

 All yield the 5-1 A (axial) and 10 A side spacing. 



Current crystallographic analysis 



A decisive step in the approach to the problems of the structure of the 

 fibrous proteins was ushered in by the proposal of helical structures by 



