132 THE PROTEIN SUBSTANCES. 



The older view that in peptic digestion only proteoses and peptones, 

 but no simpler cleavage products, are formed, has been shown not to be 

 true. The works of ZUNZ, PFAUNDLER, SALASKIN, LAWROW, LANG- 

 STEIN/ and others have shown that by very lengthy digestion amino- 

 acids may in part be formed and also other products such as oxyphenyl- 

 ethylamine, tetra- and pentamethylenediamine. The biuret reaction 

 does not disappear and the above mentioned products seem to be formed 

 only under special conditions. In ordinary, not too lengthy pepsin, 

 digestion, it is generally admitted that no amino acids are formed but 

 only proteoses and peptones. 



In connection with the above-mentioned experimental results it must be 

 remarked that not all the products found, for example, the oxyphenylethylamine 

 and the diamines, are produced by the action of pepsin, but rather by the action of 

 other enzymes. In certain cases, undoubtedly, impure pepsin was used, or indeed 

 autodigestion of the stomach was carried on, and the action of other enzymes 

 was not excluded. In other cases the digestion with pepsin and considerable 

 acid (even 1 per cent H 2 S04) was continued for a very long time, indeed for an 

 entire year, without controlling the influence of the acid alone upon the proteoses. 



KUHNE'S view that in tryptic digestion (pancreatic digestion) a 

 peptone, so-called antipeptone, always remains which cannot be further 

 split is not strictly true. By sufficiently long autodigestion of the pan- 

 creas, KuTSCHER 2 was able to obtain, as final products, a mixture of 

 digestion products which failed to respond to the biuret test, and the same 

 results have been obtained by others. An antipeptone in the old sense, 

 i.e., a digestion product which is resistant to tryptic digestion but which 

 still gives the biuret test, is* without question not always obtained as end 

 product in trypsin digestion. On the contrary as FISCHER and ABDER- 

 HALDEN 3 have shown, polypeptide-like bodies are produced in tryp- 

 tic digestion (and the same is probably true also for peptic digestion) 

 which do not give the biuret test, i.e., ".abiuret" products, and which 

 are resistant to further tryptic digestion but yield amino-acids on 

 hydrolysis with acids. This behavior stands in close relation to the 

 observation that in tryptic digestion certain amino-acids, such for example, 

 as tyrosine, tryptophane and leucine are split off earlier and more readily 

 than the others of the protein molecule. 



Antipeptone, which is only attacked with great difficulty by trypsin 

 has in fact been isolated by SIEGFRIED (see below) and although the 



1 Zunz, Zeitschr. f. physiol. Chem., 28, and Hofmeister's Beitrage, 2; Pfaundler, 

 Zeitschr. f. physiol. Chem., 30; Salaskin, ibid., 32; Salaskin and Kowalewsky, ibid., 

 38; Lawrow, ibid., 33; Langstein, Hofmeister's Beitrage, 1 and 2. 



2 Zeitschr. f. physiol. Chem., 25, 26, 28, and ,Die Endprodukte der Trypsinver- 

 dauung; Habilitationsschrift Strassburg, 1899. 



3 Zeitschr. f. physiol. Chem., 39. 



