JOHN H. NORTHROP 



603 



in substrate concentration but increases much more slowly in high 

 concentrations. Experiment 2, (Curve II) shows the same result. 

 It was made the same way but at a pH of 1.6. The points in this 

 case are the average of two determinations. They are therefore more 

 reliable and as the figure shows also more nearly equal. In both ex- 

 periments the relative activities of the two pepsin solutions were as 

 4.7: 1. It follows from the experiments that this ratio is also inde- 



TABLE I. 



Influence of Pepsin Concentration on Relative Rate of Digestion of Protein Solutions. 



Rate of hydrolysis of 15 per cent albumin 



Ratio: — : r with 



Rate of hydrolysis of 1 per cent albumin 



Rate of hydrolysis with . 08 per cent pepsin . 



Ratio: ' r~ m 



Rate of hydrolysis with . 008 per cent pepsin 



pendent of the substrate concentration in which the tests were made. 

 (It was shown in a previous paper" that the discrepancy in the rate 

 of digestion as compared with the enzyme concentration can be quan- 

 titatively explained on the basis of a mass action equihbrium between 

 the pepsin and peptone.) Table I shows a similar experiment in 

 which several duplicate determinations were made at two protein 

 concentrations with two enzyme concentrations. The results are 

 more accurate and also in closer agreement than those shown in Fig. 1. 



