ALBUMINS OR PROTEINS. 167 



The following diagram will give an idea of the hydrolysis brought about 

 by means of the pancreatic ferment, trypsin: 



Protein 



1 



'Peptones- 



A mixture of complicated compounds 

 composed of various amino acids. 

 " Polypeptides." 



Tyrosine, tryptophane, cystine, alan- 

 ine, aminovaleric acid, leucine, 

 aspartic acid, glutamic acid, histi- 

 dine, lysine, and arginine. 



The product consisting of amino acids still combined with one another, 

 and which may for the present be designated as " polypep tides," is dif- 

 ferent in the case of different proteins. In the case of edestin the amount 

 is smaller than in the case of casein, and that obtained from the latter 

 is less than from serum-globulin. 



From the investigations of Abderhalden and Reinbold, 1 it has been 

 clearly shown that, even the peptones, which still give the characteristic 

 red biuret reaction, do not immediately break down into amino acids. 

 There are certainly intermediate products between the peptones and the 

 amino acids. Here, again, the progressive decomposition is clearly 

 evident. Doubtless the simpler peptides, which we will shortly discuss, 

 also appear as intermediate products. We shall return to this shortly. 



The most important result obtained from these investigations is, that 

 the amino acids, which split off from albumin by the action of alkalies and 

 acids, are already formed in the albumin molecule and are not formed by 

 a secondary process; and, further, that in spite of the early appearance of 

 crystalline cleavage-products, the fermentative decomposition need not 

 necessarily be far advanced. All the tyrosine occurring in a digesting 

 mixture can be detected, even if, for instance, only seven per cent of the 

 amount of glutamic acid occurring in the albumin has been set free. 



Besides pepsin and trypsin, we have to consider erepsin, which occurs in 

 the alimentary tract as an albumin-splitting ferment, and has been isolated 

 by 0. Cohnheim. 2 It does not act on the proteins themselves, but only 

 on their decomposition products, the peptones. The only exceptions 

 to this rule are casein, protamines, and histons; these are attacked 



1 Loc. cit. 



2 O. Cohnheim: Z. physiol. Chem. 33, 451 (1901); 36, 134 (1902). Cf. also S. 

 Salaskin: ibid. 35, 419 (1902). 



