498 EFFECT OF ENZYME ON DIGESTION OF PROTEINS 



the enzyme combines with one (at least) of the products of reaction 

 its presence must necessarily affect the equilibrium point. The re- 

 action, therefore, would appear to be a special case of bimolecular re- 

 action in which one of the reacting substances (the enzyme) forms a 

 highly dissociated compound with one of the products. The truth of 

 the matter probably is that so called pure catalytic reactions are 

 merely limiting cases in which the combination of the catalyst is so 

 small as to escape detection (Stieglitz).^ 



SUMMARY. 



1. In certain cases the rate of digestion of proteins by pepsin is 

 not proportional to the total concentration of pepsin. 



2. It is suggested that this is due to the fact that the enzyme in 

 solution is in equilibrium with another substance (called peptone for 

 convenience) and that the equilibrium is quantitatively expressed by 

 the law of mass action, according to the following equation. 



Concentration pepsin X concentration peptone 



Concentration pepsin-peptone 



= K 



It is assumed that only the uncombined pepsin affects the hydrolysis 

 of the protein. 



3. The hypothesis has been put in the form of a differential equa- 

 tion and found to agree quantitatively with the experimental results 

 when the concentration of pepsin, peptone, or both is varied, 



4. Pepsin inactivated with alkali enters the equilibrium to the same 

 extent as active pepsin. 



5. Under certain conditions (concentration of peptone large with 

 respect to pepsin, and concentration of substrate relatively constant) 

 the relative change in the amount of active pepsin is inversely pro- 

 portional to the concentration of peptone and the equation simplifies 

 to Schiitz's rule. 



6. An integral equation is obtained which holds for the entire 

 course of the digestion (except for the first few minutes) with varying 

 enzyme concentration. This equation is identical in form with the 

 one derived by Arrhenius^® for the action of ammonia on ethyl acetate. 



7. It is pointed out that there are many analogies between the ac- 

 tion of pepsin on albumin solutions and the action of toxins on an 

 organism. 



