THE COMBINATION OF ENZYME AND SUBSTRATE. 



I. A Method for the Quantitative Determination of Pepsin. 

 11. The Effect of the Hydrogen Ion Concentration. 



By JOHN H. NORTHROP. 

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



(Received for publication, July 7, 1919.) 



I. A Method for the Quantitative Determination of Pepsin. 



Considerable experimental evidence has been obtained by various 

 authors to show that enzymes are removed from their solutions by 

 insoluble substances.^ -^ Pepsin has been especially studied from this 

 view-point. Dauwe^ showed that this property of removing pepsin 

 from its solution was not common to all substances and was connected 

 in some way with the digestive action of the enzyme. He was also 

 able to show that the size of the particles, at least in the case of egg 

 albumin, was without any marked effect on the amount of pepsin^ 

 removed. 



Abderhalden'' and his coworkers state that pepsin is removed almost 

 completely from its solution by insoluble proteins on which it acts 

 and they consider that this plays an important role in the kinetics 

 of the reaction. These results were partially confirmed by Leary 

 and Shieb.^ 



^ For the literature see Bayliss, W. M., The nature of enzyme action, London, 

 3rd edition, 1914. 



2 Nelson, J. M., and Grififin, E. G., /. Am. chem. Soc, 1916, xxxviii, 1111. 



^ Dauwe, F., Beitr. chem. Physiol, u. Path., 1905, vi, 426. This paper reviews 

 the earlier work. 



^ Abderhalden, E., and Steinbeck, E., Z. physiol. Chem., 1910, Ixviii, 293. 

 Abderhalden, E., and Strauch, F. W., ibid., 1911, Ixxi, 315. Abderhalden, E., and 

 Wachsmuth, F., ibid., 339. Abderhalden, E., and Friedel, F., ibid., 449. 

 Abderhalden. E., and Kramm, F., ibid., 1912, Ixxvii, 462. 



^ Leary, J. T., and Shieb, S. H., /. Biol. Chem., 1916-17, xxviii, 393. 



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