THE CHEMISTRY OF THE PROTEINS 119 



acids are removed and the residue treated with ammonia. A 

 substance crystallised out, which was found to be identical 

 with the diketopiperazine formed from glycine and alanine. 

 On hydrolysis it yielded glycine and d-alanine, but whether it 

 was glycyl-d-alanine or d-alanylglycine could not be exactly 

 determined, but most likely it is the anhydride of glycyl-d-alanine, 

 as the product is not hydrolysed by trypsin. 



At the same time another dipeptide, glycyl-1-tyrosine, was 

 mentioned, but its constitution was only determined later. Its 

 anhydride has been found to be identical with the synthetical 

 glycyl-1-tyrosine anhydride, and it occurred mixed with the 

 glycyl-d-alanine anhydride obtained in the above manner. 

 Glycine and 1-tyrosine resulted on hydrolysis. 



By the same method, the anhydride of glycine and leucine 

 has been prepared from elastin ; it corresponded exactly to 

 glycyl-1-leucine anhydride. To these three dipeptides, a fourth 

 must be added. It is described by Levene and Beatty as 

 prolylglycine anhydride and was obtained from gelatine. 



Further, a crystalline substance, probably a dipeptide, which 

 gives proline and phenylalanine on hydrolysis, has been isolated 

 from the products of the acid hydrolysis of gliadin by Osborne 

 and Clapp. 



The protones, which are obtained from the protamines by 

 digestion, have a molecular weight of about 420. Just as in 

 the protamines, eight-ninths of their nitrogen is in the form of 

 arginine. Kossel therefore believes that they are mixtures of 

 tripeptides, such as diarginylalanine, diarginylserine, etc., which 

 have the molecular weights of 401 and 417 respectively. 



Leucinimide, leucylleucine anhydride, described many years 

 ago by Bopp, has not yet again been isolated, and, according to 

 Fischer, its existence is doubtful. 



The work of Emil Fischer emphasises most strongly the 

 importance of the knowledge of organic chemistry to physio- 

 logical chemistry, in which branch the proteins are generally 

 studied. There is in reality no absolute difference between the 

 two subjects ; physiological chemistry deals with the question 

 how these substances are made, and what changes they undergo, 

 in nature, whereas organic chemistry treats of the changes they 

 can be made to undergo by various chemical means in the 

 laboratory, and how they can be synthesised. Synthesis also 

 occurs in nature, but whether it proceeds in a manner similar to 



