THE EFFECT OF THE CONCENTRATION OF ENZYME ON 

 THE RATE OF DIGESTION OF PROTEINS BY PEPSIN. 



By JOHN H. NORTHROP. 



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

 (Received for publication, February 16, 1920.) 



The study of the kinetics of enzyme action has led almost invariably 

 to results differing more or less from those predicted by the general 

 laws of chemistry. It would be expected from the general theory of 

 chemical reactions that enzyme reactions should conform to the law 

 expressing the rate of a monomolecular reaction, accelerated by the 

 presence of a catalyst. The rate of reaction, therefore, should be 

 proportional to the concentration of the enzyme and of the substrate 

 and should decrease with time as predicted by the monomolecular 

 formula. This has been found to be true in rare instances^ '^j but in 

 general the monomolecular formula does not hold for enzyme reac- 

 tions. It has been found in many cases that the products of reaction 

 interfere with the action of the enzyme. This would account for 

 the divergence of the rate of reaction from that predicted by the mono- 

 molecular formula, since, owing to the action of the products, the 

 concentration of the enzyme is changing during the course of the re- 

 action, while the monomolecular formula takes account only of the 

 changes in concentration of the substance decomposed. The rate of 

 reaction of two solutions containing different amounts of enzyme, 

 however, if compared during the same stage of the reaction, should be 

 porportional to the quantity of enzyme, since any effect of the prod- 

 ucts should be the same in both solutions. It is found in many in- 

 stances that this is not the case. Enzyme reactions diverge from the 

 expected course of such reactions not only as regards the change in 

 rate with the progress of the reaction, but also in regard to the re- 

 lation between the rate and the concentration of substrate or enzyme. 



1 Euler, H., Z. physiol. Chem., 1907, li, 213. 



2 Taylor, A. E., /. Biol. Chem., 1906-07, ii, 87. Also Schmitz, H., /. Gen, 

 Physiol., 1919-20, ii, in press. 



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