THE INACTIVATION OF TRYPSIN. 



II. The Equilibrium between Trypsin and the Inhibiting 

 Substance Formed by Its Action on Proteins. 



By JOHN H. NORTHROP. 

 (From the Laboratories of The Rockefeller Institute for Medical Research.) 



(Received for publication, November 15, 1921.) 



The Equilibrium between Trypsin and the Inhibiting Substance. 



The experiments already described^ show that it is possible to pre- 

 pare a solution by the action of trypsin on a protein which inhibits the 

 action of trypsin. It has also been shown that the amount of this 

 retardation can be quantitatively measured by comparing the times 

 necessary to cause a given small change in the conductivity of the 

 gelatin solution under the conditions adhered to. 



A number of hypotheses may be proposed that will account quali- 

 tatively for this retardation. The simplest would be to assume that 

 the inhibiting substance combined with trypsin to form a compound 

 that is inactive and that the activity of the solution is proportional 

 to the concentration of free trypsin remaining in the solution. It 

 has already been shown that if pure trypsin and protein is used the 

 velocity of hydrolysis is proportional to the amount of trypsin taken. 

 This is the experimental fact and is independent of any hypothesis as 

 to the kinetics of the reaction. If it is further assumed that the 

 equilibrium is governed by the law of mass action it is possible to test 

 this hypothesis quantitatively. This has been done in the following 

 experiments. 



Influence of the Order of Mixing and of the Time of Standing on the 



Eguilibriufn. 



Since in most of the experiments the retarding effect of the inhibit- 

 ing solution has been determined by adding the solution to the gelatin 



1 Northrop, J. H., J. Gen. Physiol., 1921-22, iv, 227. 



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