RECENT WORK ON PROTEIN-HYDROLYSIS 431 



however, to contain a new product, a derivative of peptone, 

 which, when acted upon by hydrochloric acid, readily yielded 

 the acid in considerable quantity. 



This new substance, which the authors call a polypeptide, 

 is easily precipitated by phosphotungstic acid, by which means 

 it can be separated from the amino-acids. By repeated solution 

 and reprecipitation by the same reagent it can be purified to a 

 considerable extent. It then gives no biuret reaction, or only a 

 very faint one. This shows, of course, that it is not the 

 ordinary peptone. On its hydrolysis with hot hydrochloric acid 

 it gives rise to a-pyrrolidin-carboxylic acid and phenylalanin, 

 as well as to certain quantities of the ordinary amino-acids, 

 leucin, glutaminic and aspartic acids, etc. It is uncertain 

 whether lysin and the other basic bodies are formed also. 



When casein was subjected to the successive action of 

 pepsin and " pancreatin " (presumably trypsin), the polypeptide 

 was found to occur, but side by side with it were small 

 quantities of a-pyrrolidin-carboxylic acid and phenylalanin. 

 The polypeptide was found to be slightly alkaline, to give a 

 reddish-purple colour with a very little dilute cupric sulphate, 

 and a precipitate with tannin, with platinic chloride, and with 

 alcohol. 



These results appear very far-reaching. In the first place 

 they point to peptone not splitting primarily into the amino- 

 acids, as taught by Kiihne, but rather yielding a polypeptide 

 of definite constitution intermediate between them, adding thus 

 another member to the classes of proteids. 



Then they indicate a very intimate association between 

 pepsin and trypsin in the working of the body. By their 

 successive actions the formation of members of the phenylalanin 

 group is effected, though by the action of trypsin alone the 

 process seems to be arrested at the polypeptide stage. 



It is clear that further investigation is called for here, for the 

 action of pepsin precedes that of trypsin, while in the formation 

 of the phenylalanins by the successive action of trypsin and 

 acid, the last stage is effected by the latter and is apparently 

 due to it. 



It is interesting to note with reference to the occurrence of 

 the polypeptide in the course of the zymolysis, that according to 

 the same writers several of the polypeptides which they have 

 succeeded in synthesising are capable of digestion by pancreatic 



