220 THE HYDROLYZING ENZYMES 



Among the Proteolytic Enzymes we again meet with a series of specific 

 relationships between the enzymes and the substances which they 

 hydrolyze. This specificity is not revealed when we act upon Proteins 

 with various Trypsins since every protein which is soluble contains 

 some of the linkages which are susceptible to attack by any given 

 trypsin. Digestion of a protein w r ill therefore proceed with trypsin 

 from any source, and if the linkages in the molecule which are attacked 

 differ with the type of trypsin employed, we have at present no certain 

 means of ascertaining that fact in so complicated a molecule as that of a 

 protein. It was for this reason that the specificity of different trypsins 

 was until recently totally unsuspected, and it was tacitly assumed 

 that all of the enzymes which hydrolyze native proteins to amino- 

 acids in faintly alkaline solutions were identical. The employment of 

 synthetic Peptides of known structure and configuration as substrates, 

 however, has recently revealed to us a heretofore unsuspected multi- 

 plicity of protein-hydrolyzing enzymes. 



The trypsin in pancreatic juice was found by Fischer and Abder- 

 halden to hydrolyze certain synthetic peptides while others remain 

 unattacked. The various peptides which they investigated were 

 distributed between these two classes as follows: 



HYDROLYZED. 



*Alanyl-glycine *Alanyl-leucyl glycine 

 *Alanyl-alanine Dialanyl-cystine 



*Leucyl-isoserine Dileucyl-cystine 



Glycl-1-tyrosine Tetraglycl-glycine 

 Leucyl-1-tyrosine Triglycl-glycine ester 



*Alanyl-glycyl-glycine d-alanyl-d-alanine 



*Leucyl-glycyl-glycine d-alanyl-1-leucine 



*Glycyl-ieucyl-alanine 1-leucyl-l-leucine 



l-leucyl-d-glutamic acid 



NOT HYDROLYZED. 



Glycyl-alanine Leucyl-proline 



Glycyl-glycine Diglycyl-glycine 



Leucyl-alanine Triglycyl-glycine 



Leucyl-glycine Dileucylglycyl-glycine 



Aminobutyryl-glycine d-alanyl-1-alanine 



Valyl-glycine 1-alanyl-d-alanine 



Glycyi-phenylalanine 1-leucyl-d-leucine 



d-leucyl-1-leucine 



It will be observed that especially among the various dipeptides formed 

 by the union of d- and 1-alanine with d- and 1-leucine the specificity of 

 the enzyme is very strongly marked. It will be noted also that mere 

 length of the pep tide-chain confers upon it susceptibility to attack. 

 Thus diglycyl-glycine and triglycyl-glycine were not attacked, while 

 tetraglycylglycine was hydrolyzed. The compounds marked with an 

 asterisk were racemic, and in every case only one of the optical anti- 

 podes was attacked, in every case also the isomer which was hydrolyzed 

 was that which occurs in the native proteins. 



