JOHN / NORTHROP 273 



tion was not markedly effected -i))^ variations in the pH of the solution 

 in the range of pH 6 to IQ. -^' 



The mechanism which iias been found to agree with the experiment 

 described in this paper will also accoimt for a peculiar fact which has 

 been frequently observed in the study of the destruction of enzyme; 

 namely, that the rate of decomposition at any one concentration will 

 be strictly monomolecular, but that the rate becomes increasingly 

 greater the more dilute the solution, instead of being independent of 

 the concentration as i?; demanded by the monomolecular formula. 

 If, as has been shown ' be true for trypsin, the rate of decomposition 

 depends on the amo of uncombined enzyme, it follows that the 

 more dilute the solution the more rapidly the enzyme will become 

 inactivated since the enzyme-inhibitor compound dissociates with 

 increasing dilution. If, further, the inactivated enzyme reacts with 

 the inhibitor to the same extent as does active enzyme (which was 

 found to be the case with pepsin) then the rate of decomposition wiU 

 be strictly monomolecular at any one concentration but will be the 

 greater the more dilute the solution. This is the experimental result. 



SUMMARY. 



1. The rate of inactivation of purified trypsin solutions approxi- 

 mates closely that demanded by the monomolecular formula. The 

 more carefully the solution is purified the closer the agreement with 

 the formula. 



2. The products formed by the action of trypsin on proteins renders 

 the trypsin more stable. Gelatin and glycine have no effect. 



3. The rate of inactivation of trypsin solutions containing these 

 products does not ^ollow the course of a monomolecular reaction but 

 becomes progressively slower than the predicted rate. 



4. The protective action of these substances is much greater if 

 they are added all at once at the beginning of the experiment than if 

 they are added at intervals. 



These observations may be quantitatively accounted for by the 

 hypothesis that a compound is formed between tr^-psin and the inhibit- 

 ing substance which is stable as well as inactive, and that the rate 

 of decomposition depends on the amount of uncombined trypsin 

 present. 



