JOHN H. NORTHROP 



243 



solution. The figure and Table V show that the retardation is nearly 

 independent of the stage of hydrolysis compared for the first part of 

 the reaction but then becomes relatively less. The retardation may 

 therefore be calculated from the velocity of the reaction provided 

 the early part of the reaction curves are compared. (It has been 

 found by Simons^^ in Nelson's laboratory that this is not the case 

 with invertase.) The result found with trypsin, namely, that the 

 retarding effect of the inhibiting solution becomes less as the reaction 

 proceeds, is exactly what would be expected if it is supposed that 

 the inhibitor combines with the enzyme to form an inactive com- 



TABLE V. 



Influence of Inhibitor on Rate of Hydrolysis Followed by Formal Titration and by 



Conductivity, 

 Temperature, 33"^C. 2.0 per cent gelatin, pH 6.2 + NaOH. Specific con- 

 ductivity, 2.2 X 10-3. 



pound and that more of the inhibiting substance is formed during 

 the hydrolysis (or some of the trypsin destroyed). The retard- 

 ing effect of the inhibiting substance formed during the reaction will 

 evidently be much less in the solution that already contained the 

 inhibitor than in the solution which contained only free trypsin. 

 The inhibitor acts just as a "buffer" solution for regulating the hydro- 

 gen ion concentration, except that in this case it is the enzyme that 

 is "buffered." In fact the same experiment may be performed by 

 following the hydrolysis of gelatin with a weak as compared with a 



^* Simons, L. S., Dissertation, Columbia University, 1921. 



