ORDER IN WHICH AMINO-ACIDS ARE SPLIT 385 



In addition it was observed that d-glutamic acid, d-tryptophane, 

 1-diamino-trioxydodecanic acid, d-1-aminobutyric acid and phenyl- 

 alanin depress the rate of hydrolysis. 



In every case it will be observed that the effects of optical 

 antipodes are considerably different, in quantity or even, in the 

 case of alanin, in sense, from one another and that the racemic 

 body affects the hydrolysis in an intermediate manner. Of 

 great significance is the fact that 1-tyrosin, which is itself a prod- 

 uct of the hydrolysis of glycyl-1-tyrosin, strongly retards the 

 hydrolysis, although glycoeoll, which is the other product, does 

 not. Abderhalden and Gigon attribute this to a binding of the 

 ferment by the tyrosin. The affinity between glycoeoll and the 

 ferment is slight and so this product does not retard hydrolysis 

 so markedly. It is possible that the low degree of affinity be- 

 tween glycoeoll and the majority of the proteolytic ferments is 

 responsible for the difficultly digestible character of many of the 

 peptids which are rich in glycocoU. 



The influence of temperature upon the rate of hydrolysis of 

 glycyl-1-tyrosin and d-1-leucyl-glycin by liver and pancreas- 

 extracts has also been studied by Abderhalden, Caemmerer and 

 Pincussohn (2). In each case, within certain limits, the rate of 

 hydrolysis is very greatly accelerated by a rise in temperature. 

 Very high temperatures, naturally, delay or prevent hydrolysis 

 by destruction of the enzyme. For liver extract, working upon 

 these substrates, the temperature-optimum proved to be about 

 55 degrees; for pancreas-extract between 45 and 50 degrees. 



3. The Order in which Amino-acids are Split off from Poly- 

 peptids by Proteolytic Ferments. — The optical properties of 

 certain polypeptids and of their possible decomposition-products 

 have been utilized by Abderhalden and Koelker (4), Abderhalden 

 and Brahm (1) and Abderhalden, Koelker and Medigreceanu (5) 

 in the attempt to ascertain which point in a tri- or tetra-peptid 

 is first attacked by a proteolytic ferment. Thus 1-leucyl-glycyl- 

 d-alanin has a molecular rotation * of +52 degrees. It might 

 conceivably yield in the first place either 1-leucyl-glycin (+172 

 degrees) and d-alanin (+2 degrees), or else glycyl-d-alanin ( — 73 

 degrees) and 1-leucyl ( — 13 degrees), or else, through simultaneous 

 spHtting of both — NHOC— bonds, all three of the products 



* The rotations given are 1/100 of the molecular rotations. Cf. Koelker 



a4). 



