u 



KERATIN AND KERATINIZATION 



show a significant constancy in the molecular ratios of histidine to 

 lysine to arginine (1:4:12), and thought that this pointed to some 

 underlying structural feature that was quite characteristic of the group. 

 More recent and more accurate analyses appear to cast doubt on the 

 integral nature of the ratios. Their approximate values are, however, 

 useful in distinguishing analytically between the hard keratins (1:4:12) 

 and the soft keratins (1:4:4) (see p. 65) and between keratins and other 

 insoluble and ill-characterized proteins. 



rrrrrrm merino 64S wool 



■HB MERINO 70S WOOL 



5CORRIEDALE 56 S WOOL 



ALA AG A P AMIDE CYS 6LU GLY HIS iSOLEU LEU LYS MET PHE PRO SER THR TRY TYR VAL 



Fig. 15. Amino acid composition of one hydrolysate from each of Merino 

 64's, Merino 70's and Corriedale 56's quality wools. From Simmonds 

 (1955). The figure shows in graphical form the analyses by Simmonds 

 of three different wools in which a considerable variation in composition 

 is apparent. 



When the best of the more recent analyses are compared (see Tables 

 1 and 2) it seems clear that: (a) very considerable differences exist between 

 some keratins and others and (b) smaller but definite differences exist 

 between different samples of similar materials, e.g. between different wools 

 (Fig. 15). Differences in cystine content are frequently reported even when 

 other acids were not determined. In the case of big differences, e.g. 

 between wool (hair), feather and epidermis, this can only mean that we 

 are dealing with rather different proteins although all may be keratinized. 

 The difference between feather and the other tissues is also revealed by its 

 different X-ray pattern (p. 16). For the a-type keratins we have accurate 

 figures only for several wools and hairs. These reveal closer similarities, 

 but even apart from cystine, no exact identity. Is there a unique ac- 

 keratin? None of the analyses suffices to prove such a protein exists. 



The thorough study of the amino acid composition of the protein found 

 in the various morphologically distinct parts of feather: calamus, rachis, 



