POLYPEPTIDES 69 



The enzymes of the various organs of the animal body havehydro- 

 lysed with few exceptions all the polypeptides upon which their effect 

 has been studied, but decided differences are noticeable. These 

 enzymes are not so selective in their action as pure pancreatic juice ; it 

 was previously found that leucyl-alanine was hydrolysed by an extract 

 of pancreas, but not by the pure juice ; glycyl-glycine is not hydrolysed 

 by trypsin, but it is attacked by an extract of liver. Leucyl-leucine 

 was not hydrolysed by the enzymes of the liver of the ox ; in all pro- 

 bability this was due to the insolubility of the dipeptide. Another 

 striking result is that glycyl-1-tyrosine was not hydrolysed by the 

 enzymes of calfs brain, which attacked the other polypeptides upon 

 which it was tested. The only diketopiperazine investigated was 

 glycine anhydride, and this was not converted into glycine. This re- 

 sult would point to the absence of anhydrides in the products absorbed 

 from the intestine. In general, the enzymes of the organs are more 

 powerful than trypsin and less selective in their action. 



H. Fischer has described the hydrolysis of d-leucyl-1-tryptophane 

 by liver extract and yeast extract. The result is contrary to what was 

 expected as the compound contains in its molecule the unnatural isomer 

 of leucine. Abderhalden attributes the result to the presence of some 

 racemic compound in the specimen employed. Racemic polypeptides 

 are generally hydrolysed asymmetrically, the polypeptide containing 

 the unnatural isomer remaining unattacked. 



The proteoclastic enzymes occurring in the germinating seeds of 

 wheat and lupine appear, according to the results obtained by Abder- 

 halden and Schittenhelm, to have a stronger hydrolytic action than 

 trypsin, since they break up glycyl-glycine and dl-leucyl-glycine, which 

 are unaffected by the enzyme of the pancreas. The enzymes in the 

 mushroom and various moulds, although they do not hydrolyse glycyl- 

 1-tyrosine, are able to hydrolyse polypeptides which are not attacked 

 by trypsin. They were tested with the racemic polypeptides and they ap- 

 parently attack both isomers ; glycyl-1-tyrosine seems to be destroyed 

 by other enzymes in the mushroom (Abderhalden and Rilliet, Abder- 

 halden and Pringsheim). The Allescheria mould will grow on media 

 containing various polypeptides as its source of nitrogen. 



The most interesting and astonishing facts were obtained by the 

 examination of the blood corpuscles, the plasma and serum. Red blood 

 corpuscles and platelets of the horse (but not of the ox) hydrolysed 

 glycyl-1-tyrosine, which was not attacked by white corpuscles obtained 

 from lymph or from pus cells, nor by the plasma or serum. Plasma 



