118 



COMBINATION OF ENZYME AND SUBSTEATE 



and further that ten to fifteen determinations can be made in the 

 course of 1 to 2 hours depending on the amount of pepsin present. 



It was now possible to determine quantitatively the amount of 

 pepsin removed from solution by various substances. 



Table II shows the results of such a series with coagulated and 

 dried egg albumin. The control experiments show that the decrease 

 in the amount of pepsin is not due to the destruction of the pepsin 

 on standing or to the retarding effect of the products of reaction. 



TABLE II. 



Change in Concentration of Pepsin in Various Solutions. 



Temperature 25°C. 



pH of all solutions, 2.5. 



1 cc. of solution pipetted off and pepsin estimated at time noted. 



* This is an experimental error. The curve was irregular and gave widely 

 divergent results for different intervals. 



A series of experiments was now made with various substances. 

 The results are summarized in Table III. It is obvious that the 

 removal of the pepsin is not purely a matter of surface but that it 

 is dependent in some way on the substance itself.^^ 



This fact is brought out more strongly in the experiments sum- 

 marized in Table IV and Fig. 2, where coagulated egg albumin of 

 different sized particles was used. It is evident that the equilibrium 



11 The author does not doubt the existence of adsorption or concentration in the 

 surface layer in the sense of Willard Gibbs. This phenomenon, however, is evi- 

 dently of subordinate importance here. 



