250 INACTIVATION OF TRYPSIN. II 



mained constant at 6.3, and the same initial conductivity. 1 cc. of 

 trypsin solution, also of the same pH and conductivity, was then 

 added in each tube and the time required to cause a change of 10 

 points in the bridge reading determined as already described. The 

 experiments show that the addition of the first cubic centimeter of 

 inhibiting solution has a much greater effect than the subsequent 

 ones and that the effect constantly diminishes and becomes apparently 

 asymptotic. This is evidently the cause of the phenomenon noted 

 earlier that the rate of hydrolysis of a solution already containing 

 some inhibiting substance is less rapidly retarded during the progress 

 of the reaction than one which contains only "pure" trypsin. This 

 is in qualitative agreement with the result predicted by the law of 

 mass action. In order to apply this law quantitatively we may proceed 

 as follows. It has been assumed that the equilibrium was expressed 

 by the eqtiation 



trypsin + inhibitor ^ trypsin-inhibitor 



and that the rate of hydrolysis was proportional to the concentration 

 of the free trypsin. The law of mass action applied to this equilib- 

 rium states that 



Concentration of free trypsin X Concentration of free inhibitor _ 

 Concentration of trypsin-inhibitor 



or 



Q r d-iE-Q) -i 



Vl V J 

 which may be written 



E-Q 



V 



= K 



IE^Tq) -KV-K (1) 



in which Q is the amount of free trypsin in volume, V, of the solution; 

 E, the total amount of trypsin in volume, V, of the solution; d, the 

 total amount of inhibitor in volume, V, of the solution; K, the equilib- 

 rium constant in arbitrary units; and K' , new constant equal to the 

 product of the equilibrium into the volume, d will evidently be 

 proportional to the number of cc. of inhibiting solution added and if 

 there are P units of inhibitor per cc. of inhibiting solution, d = P cc. 



