220 HYDROGEN ION CONCENTRATION AND PEPSIN DIGESTION 



1.0 N in respect to the chlorine ion but those which had been brought 

 to this concentration by the addition of salts were of course much 

 less acid than the one to which excess acid had been added. The 

 amount of digestion in all the solutions containing the same chlorine 

 ion concentration was approximately the same, however. This 

 result indicates that the controlling factor on the acid side of the 

 optimum is the anion concentration and not the hydrogen ion con- 

 centration. As a corollary of this it can be stated that the addition 

 of salt to a protein solution will cause the optimum hydrogen ion 

 concentration for digestion to be shifted to the alkaline side. This 

 was the effect noted by Michaelis and Mendelssohn.^^ 



The above question has recently been examined by Gyemant.^^ This author 

 found, however, the optimum pH for digestion remained at about pH 2.0 even 

 though the anion concentration was the same in all the solutions. He concludes 

 therefore that the decrease in the rate of digestion on the acid side of the optimum 

 is due to the influence of the hydrogen ion on the pepsin as proposed by Michaelis. 



The experiments described in this paper are complicated by the fact that the 

 egg albumin was partially precipitated by the high concentrations of salt and 

 acid used. This may account for the difference between the present results and 

 those of Gyemant. The discrepancy may also be due to the fact that Gyemant 

 followed the reaction by means of the increase in non-protein nitrogen whereas 

 the author used the increase in amino nitrogen. In view of Gyemant's results 

 and of the complicating factor of precipitation in the present experiments, they 

 cannot be considered as conclusive evidence in favor of the view that the anion 

 alone affects the digestion on the acid side of the optimum. It is possible that 

 both ions are active. It appears to the author, however, that the action is 

 exerted on the protein rather than the enzyme in view of the fact that different 

 proteins show slightly different optimum pH, and of the close connection between 

 the conductivity and rate of digestion of gelatin solutions (as described below in 

 this paper). 



The Conductivity and Rate of Digestion of Gelatin Solutions. 



It was mentioned above that determinations of the conductivity 

 of egg albumin solutions in strongly acid solution were made uncertain 

 owing to the precipitation of the protein. This difficulty is not 

 encountered with gelatin. Gelatin possesses the further advantage 

 that the rate of digestion in the very early stages may be easily fol- 



^^ Gyemant, A., Biochem. Z., 1920, cv, 155. 



