398 CHEMICAL DYNAMICS 



— COHN — linkages which are susceptible to hydrolysis by acids 

 (29) (114) (56) (2). Hence if the enzyme-preparation which we 

 employ is impure, i.e., contains an admixture of proteolytic en- 

 zymes, then the number of possible parallel reactions and number 

 of simultaneous points of attack in the protein molecule must be 

 greatly enhanced. It is probably to this fact that we must in 

 part attribute the much greater activity of organ-extracts and of 

 organs and tissues in situ than of isolated ferments in bringing 

 about the hydrolysis of proteins (133). 



In the thu'd place if the proteolytic enzymes are proteins or 

 peptids, as in many cases seems highly probable, they must be 

 subject to hj^dration and dehydration, just as the proteins are, 

 and in any case we know that they are thermolabile and subject 

 in aqueous solutions to loss of activity, which is usually attributed 

 to hydrolysis, and to modifications leading to precipitation fol- 

 lowing dehydration by concentrated inorganic salts. The pos- 

 sibility is thus indicated that the proteolytic ferments may exist 

 in two or more modifications, nor can we assume that only one 

 of these modifications is capable of reacting with the substrate, 

 or its products, and influencing the velocity with which they 

 undergo modification. The activity of the ferment in acceler- 

 ating either hydrolysis or synthesis of protein may therefore 

 vary with the conditions under which it acts and among these 

 conditions must he reckoned both the relative and the absolute con- 

 centrations of the substrate and ^products of the reaction, since they 

 must modify, through combination with them, the equilibrium 

 between any different forms of the enzyme which may exist 

 in the system. In quite general terms, however, and without 

 assuming the existence of more than one form of the ferment, 

 it may be stated that if the ferment enters, at any stage of the 

 reaction of protein-hydrolysis, into combination with the sub- 

 strate to any appreciable extent (and we shall see that in many 

 instances it does), since the final equilibrium of the reaction must 

 therefore be affected by the ferment, the ferment must to some 

 extent be used up in the hydrolysis and the activity of the ferment 

 must vary as the reaction proceeds. 



2. The Evidence for the Existence of Intermediate Com- 

 pounds between the Proteolytic Ferments and their Substrates. 



— The existence of compounds between proteins and proteolytic 

 enzymes has been estabhshed in a number of cases by a variety 



