SYNTHETIC ACTION OF HYDROLYZING ENZYMES 221 



The trypsin which is contained in red blood-corpuscles was found to 

 hydrolyze glycyl-1-tyrosine, in this respect resembling the trypsin of 

 pancreatic juice. It also hydrolyzed diglycyl-glycine, however, and 

 therefore it cannot be identical with the trypsin of pancreatic juice. 

 Blood-serum will not hydrolyze glycyl-1-tyrosine and the trypsin which 

 it contains therefore differs both from pancreatic trypsin and red-blood- 

 corpuscle trypsin, yet it will hydrolyze d-1-alanyl-glycine, diglycyl- 

 glycine and tri-glycyl-glycine. The existence of three different trypsins 

 is thus demonstrated, and from these and similar experiments we can 

 infer that the variety of animal trypsins is very great and possibly 

 coextensive with the number of different types of tissue which may 

 comprise the body of a multicellular animal. 



THE SYNTHETIC ACTION OF HYDROLYZING ENZYMES. 



When we hydrolyze such a substance as Ethyl Butyrate with the aid 

 of a non-enzymatic catalyzer, we find that the transformation into 

 ethyl alcohol and butyric acid is never complete, but stops short 

 when, in dilute solutions, about two- thirds of the ester is decomposed. 

 No matter what catalyzer we may employ, or if we allow spontaneous 

 hydrolysis to occur, or bring about hydrolysis by means of a fat-split- 

 ting enzyme, the transformation comes to a standstill when about one- 

 third of the ester still remains undecomposed. 1 On the other hand, 

 if we mix ethyl alcohol and buytric acid, and by the agency of cata- 

 lyzers or otherwise, bring about their combination, we will find that 

 here also the transformation is never complete, but that it comes to a 

 standstill when about one-third of the alcohol and buytric acid have 

 combined to form the ester. Evidently, therefore, from whichever end 

 of the process we start we reach a mixture of the same composition. 

 We cannot suppose that either reaction has then ceased to occur, but 

 we can readily see that in the mixture which no longer alters in com- 

 position and is at equilibrium the forward and reverse actions are pro- 

 ceeding at the same rate: 



C 3 H7COOC 2 H B + H 2 O ; C 3 H 7 COOH + C 2 H 6 OH 



In a variety of hydrolyses the same phenomenon is observed, but in 

 the majority of instances the station of equilibrium lies further to the 

 right or left than in the instance chosen for illustration. Thus in the 

 hydrolysis of cane-sugar it lies so far to the left that at equilibrium the 

 hydrolysis is, so far as all practicable measurements are concerned, 

 absolutely complete. 



Now a true catalyzer is, as we have seen, not consumed at all during 

 the progress of the process which it accelerates, and, this being the 

 case, it cannot communicate any Energy to the system. Any shift of 

 equilibrium in a chemical reaction which absorbs or liberates heat 

 must involve the consumption or absorption of a quantity of energy 

 equivalent to the heat of reaction. But equilibrium, as we have seen, 



1 The exact proportion depends, as we shall see, upon the dilution of the solution, 

 i. e., upon the mass of water in the reacting mixture, 



