164 KERATIN AND KERATINIZATION 



degradation are resorted to in the attempt to discover the existence of 

 macromolecular units of an intermediate range of size. The study of the 

 problem of how many polypeptides participate, the composition and length 

 of these chains and their sequence of amino acids has not progressed far. 

 The formidable difficulties of the problem are obvious. Most methods of 

 studying proteins have been developed for the soluble proteins and, to 

 apply these, we have first to develop methods of obtaining soluble deri- 

 vatives of keratin by procedures which will permit the structure of the 

 insoluble original to be inferred from that of the soluble derived fragments. 

 The solutions must be fractionated into their constituent polypeptides 

 and the location of the constituents in the original solid complex established. 

 Most of the work of this nature will be described in Chapter 6 and is 

 only mentioned here for reasons of formal completeness. Most workers, 

 accepting the view that the insolubility of keratin is due to two factors : 

 (a) the interchain cross-linking by the sulphur bridge of the cystine 

 residues, and (b) the presence of numerous hydrogen bonds, have at- 

 tempted, either in a single stage or in successive stages, to rupture both 

 classes of bonds and thus to obtain a preparation of the free, constituent 

 polypeptides (p. 233). A considerable number of preparations have in fact 

 been made, often with a view to obtaining a product of some commercial 

 value, but the few of these that have been examined in detail have not 

 proved promising sources for the extraction of pure proteins or their 

 derivatives. It is in the purification of these mixtures that a very substan- 

 tial contribution towards further progress is expected. For the present 

 we may summarize the results for wool as follows: all the materials 

 examined contain several polypeptide species probably differing in com- 

 position. There is some evidence to suggest that the derived polypeptides 

 can be grouped into two classes probably related to two distinct mor- 

 phological components, filaments and matrix, visible in electron micro- 

 graphs (Chapter 6). The proteins derived from the filaments have a 

 higher molecular weight (50,000-80,000) than those of the matrix 

 (~ 10,000); the latter contain a greater amount of the cystine residues. 

 None of the many components have been prepared in a state of complete 

 purity and little progress is possible at the moment towards forming a 

 detailed picture of the place of each in the original insoluble hair. In the 

 case of feather Woodin's 10,000 m.wt. unit has some claims to be regarded 

 as a definite monomer. 



Non-destructive Methods 

 X-ray diffraction 



Although the chemical analysis of a complex material of biological 

 origin may have only a limited value unless pure components are first 

 extracted, the X-ray analysis of the same material may bear immediate 



