272 



INACTIVATION OF ATSIN. IH 



which correctly expresses the rat*^ of decomposition. The time 

 required for a certain amount to be uestroyed could not be determined 

 owing to experimental difficulties. 



Influence of the pH on the Protective Effect of the Inhibiting Substance. 



A comparison of the curves (Fig. 5) for the dialyzed trypsin solu- 

 tion and the solution to which inhibiting substance had been added 

 shows that the protective action of the latter is also a function of the 

 pH. There is little or no protective action on the acid side of pH 5. 



cioo 



Fig. 5. Decomposition of trypsin solutions at 38°C. and different hydro- 

 gen ion concentrations. Per cent of trypsin remaining active after 0.5 hours 

 at 38°C. 



As the solution becomes more alkaline the protective action increases 

 and then decreases slightly although the experiments are hardly accu- 

 rate enough to be certain of this second decrease. If the hypothesis 

 which has been used to account for experiments so far is correct this 

 behavior evidently means that on the acid side of pH 5, trypsin does 

 not combine with the inhibiting compound and that the combination 

 has a maximum somewhere near a pH of 8 to 9. 



This experiment confirms those described in the preceding paper in 

 which it was found that the retarding influence of the inhibiting solu- 



