602 



SUBSTRATE CONCENTRATION AND HYDROLYSIS 



Fig. 1 gives the results of two experiments on the effect of the 

 pepsin concentration on the relative rate of digestion of protein 

 solutions of different concentration. In Experiment 1, (Curve I, 

 Fig. 1) 25 cc. of protein solution containing 8, 4, 2, 1, and 0.5 per cent 

 protein, were hydrolyzed at 25° with the addition of (a) 1 cc. of 2 

 per cent pepsin, and (b) 1 cc. of 0.2 per cent pepsin. All solutions 

 were brought to a pH of 1.8 with hydrochloric acid. The time nec- 

 essary to cause a given change (about 1.4 X 10"* reciprocal ohms) 

 in the specific conductivity was determined.^*' The reciprocal of this 



100 





80 



60 



40 



20 



1 2 



16 



3 4 6 8 12 



Gm. eqq albumin per 100 cc. 



Fig. 1. Relative rate of digestion of egg albumin solutions of different concen- 

 tration when digested with pepsin solutions of different concentration. 



time, therefore, gives the mean rate of digestion of the various solu- 

 tions for the first 1.4 X 10"* reciprocal ohm change. In order to 

 compare the two series, the rate of digestion of the concentrated egg 

 albumin (in each series) was considered as 100 and the rate of diges- 

 tion of the other concentrations calculated on this basis. The curve 

 shows that the relative rate of digestion of the 8 per cent egg albumiin 

 compared to the rate of digestion of 4, 2, 1, or 0.5 per cent egg 

 albumin is the same irrespective of whether 2 or 0.2 per cent pepsin 

 was used. The curve also shows that in low concentrations, 0.5 to 

 2 per cent, the increase in rate is nearly proportional to the increase 



i« Northrop, J. H., J. Gen. Physiol, 1919-20, ii, 113. 



