THE SYNTHESIS OF THE PROTEINS 47 



dog Abderhalden and Samuely added dl-leucine and racemic leticyl- 

 leucine, and Abderhalden and Babkin added leucyl-glycine. These 

 results differed from those of Wohlgemuth, who found that the rabbit 

 excreted d-leucine when dl-leucine was given, but Abderhalden and 

 Kautzsch have also found that the rabbit excretes d-leucine when some- 

 what large doses of dl-leucine are administered, whereas this animal can 

 utilise dl -leucyl-glycine and dl-leucyl-glycyl-glycine. Abderhalden has 

 since found that the rabbit excretes glycine, 1-alanine, and d-serine when 

 the diketopiperazines of these amino acids are administered, which points 

 to their hydrolysis into the dipeptide before they are split into the 

 amino acids. 



The organs of various animals, such as the dog and rabbit, would thus 

 appear to differ in their power of making use of synthetical polypeptides, 

 but the animal organism as a whole is not so selective as the enzyme 

 of the pancreas which hydrolyses the racemic dipeptide asymmetrically ; 

 in the body the racemic compound is completely burnt up, since no 

 dipeptide composed of the optically active variety of the amino acid not 

 occurring in a protein could be isolated. Further, the animal organism 

 is able to utilise polypeptides not hydrolysed by pancreatic juice, so 

 that if such polypeptides are present in the protein, they can still be 

 utilised by the body although unaffected by trypsin. 



Although these polypeptides are utilised by the organism of an 

 animal and the nitrogen contained in them excreted as urea, it does 

 not follow from the results of the experiments that these polypeptides 

 are hydrolysed into their constituent amino acids previous to absorption, 

 more especially those which are not acted upon by trypsin. 



Great interest therefore is attached to the subsequent work of Abder- 

 halden in conjunction with Teruuchi, Hunter and Rona, which was 

 commenced in 1906 upon the action of extracts and of press-juices of 

 various organs, prepared by Buchner's method of grinding up with 

 sand, mixing with Kieselguhr and pressing out at a pressure of 100-300 

 atmospheres, whereby the cell enzymes are obtained. A large number 

 of polypeptides were employed for determining the nature of these 

 enzymes in the hope of rinding differences between them, and dividing 

 the proteoclastic enzymes into definite groups, especially as we regard 

 enzymes as being extremely selective in their nature, and in the hope 

 also of determining in which organ the hydrolysis of any particular 

 polypeptide took place. An extract of pancreas was previously found 

 to hydrolyse leucy 1-alanine, which was not attacked by pure pancreatic 

 juice, but the results show that the enzymes contained in the various organs 

 are not so selective as pure trypsin in their action, and among themselves 

 .show decided differences as exemplified in the following tabulation : 



