186 LECTURE IX. 



Glycine anhydride and alanine anhydride are likewise utilized. They may 

 possibly be decomposed in the intestine, and converted first of all into 

 polypeptides. Leucyl-leucine is utilized in the same manner as leucine. 1 



The keystone of the whole proof must be regarded as certainly reached 

 if we can obtain from albumin itself products analogous to the polypeptides. 

 This has been accomplished. Its accomplishment was due entirely to 

 applying the knowledge gained concerning the synthetic polypeptides to the 

 study of the decomposition of proteins. It was found possible to act upon 

 proteins in such a way that they did not break down entirely into their 

 simplest components, the amino acids, and, on the other hand, to 

 carry the decomposition beyond the point of the most complicated cleavage- 

 products. Such a partial decomposition could be most easily accom- 

 plished by acting on those albumins on which the usual reagents, acids 

 and alkalies, and, above all, the proteolytic ferments, have least effect. We 

 have succeeded in obtaining from silk-fibroin, by a preliminary action of 

 acid in the cold and a subsequent digestion by pancreatic juice, apolypep- 

 tide in the form of its anhydride. 2 All its characteristics, and especially its 

 cleavage into d-alanine and glycocoll, as well as its conversion into the 

 polypeptide, proved that a compound was present which corresponded to 

 the polypeptide composed of d-alanine and glycine. We do not err in 

 designating it as glycyl-d-alanine. The compound was isolated as a 

 polypeptide-ester and converted into its anhydride by the action of alco- 

 holic ammonia. By splitting the glycyl- alanine anhydride we naturally 

 obtain two products depending on the portion of the piperazine ring 

 attacked; thus, glycyl-d-alanine or d-alanyl-glycine result, as is indicated by 

 the following formula: 



II 



CH 2 -CO\ NH 

 NH / / NtL 



I N CO CH-CH 3 



If the ring is ruptured at I, we obtain, by the addition of water: glycyl- 

 alanine, NH 2 . CH 2 . CO . NH . CH . CH 3 . COOH. If at II, we get alanyl- 

 glycine, NH . CH . CH 3 . CO . NH . CH 2 . COOH. 



The anhydride itself does not, therefore, give us the answer regarding 

 the form of polypeptide from which jit was produced. We do, however, 

 know that alanyl-glycine is easily separated into its constituents by trypsin, 

 whereas glycyl-alanine is not acted upon. We may, therefore, conclude 

 that the compound isolated was glycyl-rf-alanine. Then, again, this same 

 cleavage-product is formed by acid action whether by concentrated 

 hydrochloric, or 70 per cent sulphuric acid. Under these conditions, i.e. 



1 E. Abderhalden and F. Samuely: Z. physiol. Chem. 47 (1906). 

 a E. Fischer and E. Abderhalden: Ber. 39, 752 (1906). 



