120 



COMBINATION OF ENZYME AND SUBSTRATE 



case the law of partition coefficients should be found to hold, or of 

 chemical combination, in which case the law of mass action should 

 apply. Prehminary experiments indicate that the process follows 

 the law of partition coefficients. 



It may be objected that the effective surface is not the actual 

 surface of the particles but some fine interior structure which is the 

 same in all. The particles, however, swell in acid and appear trans- 

 lucent and homogeneous. It would seem that any interior surfaces 

 must be of nearly intermolecular dimensions. In this case, of course, 

 all chemical phenomena may be considered "surface" phenomena. 



m 



10 



20 



30 



40 50 eo 

 riinates 



Fig. 2. 



70 



80 



SO 



100 



//. The Efect of the Hydrogen Ion Concentration. 



Inasmuch as the activity of pepsin is dependent to a large extent 

 on the hydrogen ion concentration it appeared probable that the 

 combination of pepsin with its substrate would be a function of the 

 same variable. Table V and Fig. 3 show the results of a series of 

 experunents made at different hydrogen ion concentrations. There 

 is a decided optimum for the combination of pepsin with its substrate 

 corresponding (within the limits of error) to the optimum for digestion. 

 These experiments were repeated with casein with approximately 

 the same results. The optimum zone for the digestion of proteins 



