FERMENTS. 475 



possible that the electro-negative character of these compounds plays a 

 part. It has not yet been decided whether the easy cleavage of the two 

 cystine derivatives is due to this cause, or that the length of the chain is a 

 factor. It is very noteworthy that the dipeptides, which contain a-amino- 

 butyric acid, and leucine as acyl, offer great resistance. 



The influence of configuration is also clearly indicated in this case. The 

 polypeptides in the above table which are designated by an asterisk, are 

 racemic compounds. In all of these cases, the hydrolysis is an asym- 

 metric one, i.e., only half of the racemic body is attacked. The products 

 resulting from the hydrolysis were the same as those active amino acids 

 which are contained in the natural protein-substances. A special case is 

 shown by the contrast between the alanyl-leucine A. and alanyl-leucine B. 

 In these two racemic compounds are present all four combinations of the 

 four active amino acids. One racemic compound is d-alanyl-d-leucine + 

 Z-alanyl-Z-leucine; the other, d-alanyl-Z-leucine + Z-alanyl-d-leucine. Of 

 these four combinations, the pancreatic juice will attack only that corre- 

 sponding to d-alanyl-Z-leucine. This fact is of great significance. It 

 supplies us with a means for determining directly the configuration of the 

 synthetic polypeptides. 



The number of the amino acids contained in the complex molecule is 

 also of influence. The glycine chains give us a distinct example of this. 

 Glycyl-glycine, diglycyl-glycine, and triglycyl-glycine are not hydrolyzed, 

 while tetra-glycyl-glycine is acted upon. Leucyl-glycine, also, is not 

 decomposed, although leucyl-glycyl-glycine is. The reason that dileucyl- 

 glycyl-glycine is not decomposed, lies probably in the configuration of the 

 dileucyl group. 



If the cleavage takes place along asymmetric lines, the beginning of 

 hydrolysis in the previously inactive digesting liquid is established by the 

 appearance of optical activity. 



We may here include the observation of O. Warburg, 1 who showed that 

 the ester of racemic leucine is saponified asymmetrically by the pancreatic 

 juice. We do not know what ferment produces this result. Lipase may 

 be the active principle, as is suggested by an analogous observation of 

 H. D. Dakin. 2 



Closely related to these discoveries, is the fact previously mentioned, 3 

 that the animal organism utilizes only one-half of certain racemic sub- 

 stances, the other optical isomer being eliminated unchanged. These 

 discoveries show very clearly the similarity of " organized " and unor- 

 ganized ferments, and justify us in concluding that all ferments must be 

 considered from the same point of view. 



1 Ber. 38, 187 (1905). 



3 Proc. Chem. Soc. 19, 161 (1903); J. Physiol. 32, 199 (1905). 



3 Compare Lecture XIX, p. 452. 



