JOHN H. NORTHROP 



121 



by pepsin therefore is due to the fact that at this degree of acidity 

 more pepsin combines with the protein than in either a more or less 

 acid solution. Van Slyke and Zacharias/^ from a study of the con- 

 stants of their equation for the action of urease, decided that the 

 hydrogen ion concentration affected the rate of , combination of the 



TABLE V. 

 Ejffect of Reaction of Solution on Combination of Pepsin and Coagulated Egg Albumin. 



Experiment A. 



Temperature 25°C. 



0.5 gm. of egg albumin suspended in 10 cc. of HCl of increasing strength. 1.0 

 cc. of strong pepsin solution added. Tube shaken, allowed to stand 1 min., and 

 clear liquid pipetted off. pH measured (by gas chain) in part of this sample. 

 5.0 cc. of remainder brought to same reaction in all tubes by addition of a few 

 drops of strong HCl. All brought to same volume with water and pepsin esti- 

 mated in 1 cc. 



Experiment B. 



Same as A, but allowed to stand 2 min. 



enzyme and substrate. In the case of pepsin, however, it is not the 

 rate of combination but the amount which is influenced. This is 

 shown by the fact that Httle or no pepsin is removed from its solution 

 by its substrate at a reaction of 5.0, no matter how long they are 



^^ Van Slyke, D. D., and Zacharias, G., /. Biol. Chem., 1914, xix, 181. 



