THE CHEMISTRY OF THE PROTEINS 117 



Abderhalden to determine the nature of the proteolytic ferments 

 in the various organs, whether they contain a single enzyme 

 or a mixture. Commercial trypsin, or a dried extract of the 

 pancreatic gland, has already been seen to act differently from 

 pure pancreatic juice, and the same applies to pure gastric juice 

 and commercial pepsin. Glycyl-1-tyrosine is a very convenient 

 substance to distinguish between pepsin and trypsin, as it is not 

 split by the former, but hydrolysed by the latter to glycine and 

 tyrosine. By its means duodenal juice has been shown to contain 

 a ferment like pepsin, since it was not hydrolysed. The ferments 

 of the liver, muscle, kidney contained in the juice obtained by 

 Buchner's method of grinding with sand, mixing with kieselguhr 

 and pressing out at 300 kilograms pressure, behaved like trypsin, 

 but were more active, as they hydrolysed dl-leucylglycine, 

 glycylglycine, glycylalanine, etc. The}^ are therefore less 

 selective in their action, and consequently polypeptides contained 

 in peptone absorbed from the intestine may yet be hydrolysed 

 and assimilated by the various organs. The resultant action of 

 trypsin upon proteins is the production of amino acids and a 

 complex polypeptide (antipeptone of Kiihne). This polypeptide, 

 on absorption, will be broken down and be assimilated by the 

 different organs. 



The resistant polypeptide may contain other kinds of com- 

 bination, such as ether, ester (Warburg has found, however, that 

 trypsin acts upon leucinester), diketopiperazine, which are not 

 broken open by trypsin or pancreatic juice, but by the ferments 

 of the liver. The action of arginase upon arginine, a combina- 

 tion of ornithine and urea, which is not acted upon by trypsin, 

 as also the changes which the purine bases undergo in the liver 

 by special enzymes are examples of this kind. In the animal 

 body, the combined action of ferments plays a great part. The 

 resistant polypeptide does not appear in quite the same form 

 when the protein is acted upon first by pepsin and then by 

 trypsin. According to Cohnheim hydrolysis by pepsin followed 

 by erepsin, the ferment obtained from the mucous membrane 

 of the duodenum, produces the same result as pepsin followed 

 by trypsin. This ferment has been shown by Abderhalden to 

 hydrolyse polypeptides not acted upon by trypsin. 



It would seem, therefore, as if the study of the action of 

 pancreatic juice would not lead directly to the exact manner 

 of combination in the protein molecule, but it will, nevertheless, 



