F. SANGER 



fractionate. It would seem that the most hopeful method of 

 attacking these larger proteins would be by an initial specific 

 degradation to polypeptide chains of up to 30 residues long, 

 which could then be studied by the methods used for insulin. 

 It should not, however, be assumed that these methods will 

 automatically yield the structure of any polypeptide of 20 to 30 

 residues long. Special problems are likely to be encountered, 

 as they were in the insulin chains, and will have to be solved by 

 special methods. It does, however, appear that the main lines 

 of progress in this field will be dependent on finding specific 

 methods for degrading proteins and techniques for fractionating 

 the large polypeptides so produced. The enzymes trypsin and 

 chymotrypsin are at present the most specific hydrolyzing agents 

 and will undoubtedly be of great use in this respect, though it is 

 doubtful if they alone will be sufficient for the more complex 

 proteins. Work is at present actively in progress in this field, 

 and it is evident that in the near future we will learn much more 

 about the detailed structure of proteins and of the many bio- 

 logical processes which depend upon their structures. 



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