POLYPEPTIDES 67 



burnt up in the organism of the dog when injected into the system, 

 and Abderhalden and Samuely observed that this was also the case 

 when cystine, dialanyl-cystine and dileucyl-cystine were subcutaneously 

 introduced. Abderhalden continued these investigations with Teruuchi, 

 with the result that the organism of the dog was found to be able to 

 utilise completely glycyl-glycine, alanyl-alanine and diglycyl-glycine 

 as well as the diketopiperazines, glycine anhydride and alanine anhy- 

 dride, when they were given by the mouth, the nitrogen contained in 

 these substances being eliminated as urea. To this series of polypep- 

 tides capable of being utilised by the dog Abderhalden and Samuely 

 added dl-leucine and racemic leucyl-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 somewhat large doses of 

 dl-leucine are administered, although 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 diketo- 

 piperazines 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 poly- 

 peptides, 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 pan- 

 creatic 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 before they are ab- 

 sorbed, more especially those which are not acted upon by trypsin. 



Great interest therefore is attached to the subsequent work of 

 Abderhalden 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 outat a pressure of 100-303 



