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DOES THE KINETICS OF TRYPSIN DIGESTION DEPEND 



ON THE FORMATION OF A COMPOUND BETWEEN 



ENZYME AND SUBSTRATE. 



By JOHN H. NORTHROP. 

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



(Received for publication, March 13, 1922.) 



Trypsin, in common with many other enzymes, possesses the 

 pecuHarity that the rate of formation of the products of hydrolysis 

 does not increase in proportion^ to the substrate concentration, as is 

 demanded by the law of mass action, but increases more slowly than 

 the substrate concentration and eventually becomes nearly inde- 

 pendent of it.2 It is necessary to assume, therefore, either that the 

 mass law in its simple form does not hold or that the concentration 

 in grams per Hter does not represent the "active" concentration of 

 substrate. A very similar phenomenon is quite common in ordinary 

 catalytic reactions. In this case it has usually been assumed that 

 the mass law is valid but that the concentration to be used in the 

 calculation is not the total concentration of the substance taken but 

 that of some particular molecular species which is formed from this 

 substance in solution. In the case of acid hydrolysis, for instance, 

 the action is assumed to be equal to the concentration, not of the 

 acid itself, but of the hydrogen ions. In this case the assumption 

 is capable of verification since the concentration of hydrogen ions 

 may be determined by several independent methods which give 

 approximately the same results, all verifying the assumption. If 

 this were not the case, the kinetics of acid hydrolysis would be more 

 difficult to interpret than the kinetics of enzyme reactions. In the 

 case of enzymes, however, it has usually been assumed, following the 



1 Bayliss, W. M., Arch. Sc. Biol., 1904, xi, suppl., 261. 



2 In the case of alkali or acid hydrolysis this is not true. The rate of digestion 

 in the absence of enzyme is proportional to the gelatin concentration. See 

 Northrop, J. H., /. Gen. Physiol., 1921, iii, 715. 



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