JOHN H. NORTHROP 



271 



solutions was determined by adding 1 cc. to 50 cc. of 5 per cent gelatin 

 containing 0.2 m Na2C03 (pH = 10) and the rate of hydrolysis followed 

 by the formol titration. Trypsin is evidently most stable at a pH 

 of 5. The rate of decomposition increases quite rapidly if the solu- 

 tion is either more or less acid.'* It differs in this respect from pepsin 

 which is stable over quite a wide range and resembles the invertase 

 studied by Hudson.^ The rapid increase in the rate of destruction 



o 

 o 



(S> 



c 

 a. 



o 



12 3 



Hours at 62° 



Fig. 4. Inactivation of trypsin and trypsin-inhibitor compound at 62°C. 



with increasing alkalinity makes it evident that this behavior must 

 enter to a large extent in deciding the optimum pH for the action of 

 the enzyme. It was not found possible to determine quantitatively 

 the effect of the pH owing to the fact that the reactions are rarely 

 strictly monomolecular and it is therefore difficult to fmd a value 



* This agrees with the experiments of Ringer (Ringer, W. E., Z. Physiol. Chan., 

 1921, cvi, 107). 



* Hudson, C. S., and Paine, H. S., /. Am. Chem. Soc, 1910, xxxii, 774. 



