610 SUBSTRATE CONCENTRATION AND HYDROLYSIS 



to the law of mass action between the uncombined pepsin and the 

 protein ion. The mechanism may be formulated as below. 



or 



and 



or 



Pepsin + peptone -^ pepsin-peptone 



r ■ — -IT C^pepsin-peptone /.xjo 



*^pepsin -~ K — ^ J^ J 



Cpeptone 



Protein-chloride ^ protein"*" -\- C\~ 



C . . — T- ^--protein-chloride , t^-o 



^protein ion — J\. '-J' 



Cci- 

 The reaction would be expressed by 



Protein ion + pepsin ^ [protein ion-pepsin] ^ peptone-pepsin :;=± pepsin -f peptone 



The rate of hydrolysis of the protein at any instant of time would 

 therefore be proportional to the concentration of protein ions and 

 of free pepsin present in the solution at that instant and the differ- 

 ential expression for the rate of reaction would be 



"C-protein ion t' r* . . n 



' ' ~ "- ^protein ion • '^pepsin 



dl 



where Cprotein ion and Cpepsin are determined by equations (1)' 

 and (2). There is probably little doubt that the enzyme and sub- 

 strate unite to form an addition product, but according to the ex- 

 perimental evidence found in this paper the time during -which they 

 are combined is negligible in the consideration of the kinetics of the 

 reaction. 



The mechanism outlined above will explain, at least qualitatively, 

 the peculiarities in the kinetics of other enzyme reactions. It seems 

 very unlikely, however, that the equilibrium in the substrate solution 

 should always be ionic. It may be any isomeric equilibrium. Since, 



^^ The equilibrium expressed in (2) is certainly, and that expressed in (1) is 

 probably, influenced b}- the hydrogen ion concentration. 



