JOHN H. NORTHROP 263 



Influence of the Purity of the Solution on the Course of the Reaction. 



Fig. 1 contains the results of a series of experiments on the rate of 

 inactivation of various trypsin solutions at 38° and pH 6.2. The 

 amount of active trypsin remaining in solution at any time has been 

 plotted as the logarithm so that if the reaction were monomolecular 

 the resulting curv^e would be a straight line. As the figure shows 

 this is true in the case of the dialyzed trypsin. This particular 

 solution had been dialyzed under pressure for 18 hours at 6°C., fil- 

 tered and redialysed. The constant found is 0.005 (time in minutes 

 and common logs). This experiment could not be repeated with cer- 

 tainty but in general, the more carefully the solution was purified the 

 more nearly the reaction was found to be monomolecular. The figure 

 also shows that undialyzed trypsin solutions and those to which 

 gelatin had been added are apparently inactivated at first more 

 rapidly than the pure solutions and then much more slowly. On the 

 other hand, solutions containing inactivated trypsin or substances 

 which had been found to interfere with the action of the enzyme, are 

 much more stable, and if a large amount of these substances are pres- 

 ent amount of decomposition is too small to determine in the interval 

 of time chosen. The addition of glycine is without effect. 



It has been shown in the previous paper that the products formed 

 by the action of trypsin on proteins form a compound with the trypsin 

 that is inactive. The simplest explanation for the present experi- 

 ments would be to assume that exactly the same mechanism is at 

 work here and that the compound, trypsin-inhibitor, is stable as well 

 as inactive. It was found that the experiments referred to were in 

 quantitative agreement with the hypothesis that the trypsin and 

 inhibiting substance unite to form a compound according to the 

 equation 



trypsin + inhibitor ^ trypsin-inhibitor 



and further that this equilibrium conformed to the law of mass 

 action ; i.e. 



Concentration of free trypsin X Concentration of free inhibitor 



; = a constant 



Concentration of tiypsin-inhibitor 



