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-l-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. Theferments 
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. They 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 Ktihne). 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, 
