ii4 



SCIENCE PROGRESS 



result when the proteins are hydrolysed by the proteolytic 

 enzymes, pepsin, and trypsin. Even under identical conditions 

 it is difficult to determine how far hydrolysis has proceeded 

 under their influence, as two preparations are scarcely ever of 

 the same strength. Hydrolysis by acids and alkalies is not so 

 limited, as they tend to give the ultimate end products which at 

 the same time undergo partial racemisation. 



The study of the behaviour of the synthetical polypeptides 

 to trypsin throws much more light upon the combinations which 

 may actually occur in the protein molecule. Each protein may 

 again possess different combinations ; their properties, as also 

 the various amounts of the same amino acid, obtained by 

 hydrolysis, point to a variety of combinations. 



Fischer commenced his investigations upon this subject in 

 conjunction with Bergell at a time when only a few of the 

 dipeptides had been prepared. The hydrolysis of these by 

 trypsin was found to depend upon various factors. Further and 

 much more complete investigations were carried out with 

 Abderhalden, as the result of which the synthetical polypeptides 

 could be divided into two classes : 



Those Hydrolysed 

 *alanylglycine 

 *alanylalanine 

 *alanylleucine A 

 *leucylisoserine A 

 glycyl-1-tyrosine 

 leucyl-1-tyrosine 

 *alanylglycylglycine 

 *leucylglycylglycine 

 *glycylleucylalanine 

 *alanylleucylglycine 

 dialanylcystine 

 dileucylcystine 

 tetraglycylglycine 

 triglycylglycinester 

 (Curtius* biuret base) 



Those not Hydrolysed 

 glycylalanine 

 glyclyglycine 

 alanylleucine B 

 leucylalanine 

 leucylglycine 

 leucylleucine 

 aminobut3^rylglycine 

 aminobutyryl-aminobutyric acid A 

 aminobutyryl-aminobutyric acid B 

 aminoisovaleryl-glycine 

 glycylphenylalanine 

 leucylproline 

 diglycylglycine 

 triglycylglycine 

 dileucylglycylgiycine 



The two classes show firstly the endless variety of the 

 simple polypeptides, and secondly, on closer examination, that 



* These are racemic compounds. 



