u8 SCIENCE PROGRESS 



give us a very good insight as to a very large number of these 

 combinations. The only way to arrive at the ultimate solution 

 is the isolation of various complexes before complete hydrolysis. 

 Pick and Zunz have separated various proteoses and peptones, 

 but these are still too complex, as also are the bodies, called 

 kyrines, prepared by Siegfried. We must determine the 

 combinations of two, of three, of four, as they exist, and their 

 possible combinations with each other. A commencement has 

 already been made by Fischer and Abderhalden, who have 

 isolated three dipeptides. 



A great deal of confusion has for a long time existed con- 

 cerning the nature of the proteolytic ferments contained in 

 germinating seeds and various plants. By investigating the 

 action of these enzymes upon various polypeptides, Abder- 

 halden and Schittenhelm found the enzymes of the germinating 

 seeds of wheat and lupines contained a tryptic ferment ; and 

 Abderhalden and Teruuchi showed that the endotryptase of 

 yeast and pepsin were like trypsin in their action, whereas 

 the juice of Nepenthes contained an enzyme like pepsin in its 

 nature. 



V. The Isolation of Polypeptides from Proteins 



In 1902 Fischer described the results of some experiments 

 which he had made in conjunction with Bergell upon the 

 isolation of a dipeptide from silk by means of the combined 

 action of acid, alkali, and trypsin. By the action of hydrochloric 

 acid upon silk fibrin, a peptone is obtained which gives a marked 

 reaction for tyrosine. If this be treated with trypsin, the 

 tyrosine is completely split off, and another peptone free from 

 tyrosine results, which when acted upon by baryta, loses 

 ammonia and yields a dipeptide. This dipeptide was considered 

 to be glycylalanine, though the proof could not be satisfactorily 

 given at the time. 



This product was not again obtained until quite recently, as 

 the exact conditions of its formation could not be repeated ; 

 Fischer and Abderhalden then isolated it in the form of its 

 diketopiperazine. The silk fibrin was acted upon either by 

 sulphuric acid followed by trypsin or by hydrochloric acid ; the 

 product was esterified and distilled in the ordinary manner 

 at a low temperature, whereby the esters of the monoamino 



