THE EFFECT OF VARIOUS ACIDS ON THE DIGESTION OF 

 PROTEINS BY PEPSIN. 



By J. H. NORTHROP. 

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



(Received for publication, May 21, 1919.) 



The widespread occurrence of antagonistic salt action on living 

 tissues raises the question whether the underlying cause of the phe- 

 nomenon might not be found in the action of the salts on the activity 

 of the enzymes. A similar effect has been described by Falk^ in the 

 case of lipase. As Loeb^ -^ has shown, it is also possible to demonstrate 

 antagonistic salt action on the physical properties of a protein; i.e., 

 gelatin. It seemed important therefore to determine whether or not 

 such an effect was to be found in the influence of various acids on the 

 digestion of proteins by pepsin. 



The relative action of the various acids on the pepsin digestion of 

 proteins has already been the subject of many investigations.^ The 

 literature on the subject is confused and contradictory, however, due 

 largely to the fact that in the early work the effect of the hydrogen 

 ion concentration was not taken into account and that the acids 

 were usually compared in equimolecular or even equipercentage 

 strengths. Attempts were made by Berg and Gies^ to rule out this 

 disturbing factor by using solutions containing equal calculated 

 amounts of hydrogen ion. They took no account, however, of the 

 ''buffer" action of the weaker acids and of the proteins so that their 



1 Falk, I. S., /. Biol. Cheni., 1918, xxxvi, 229. 



2 Loeb, J., J. Biol. Chem., 1918, xxxiii, 531 ; /. Gen. Physiol., 1918-19, i, 39, 363, 

 483, 559. 



3 Loeb, J., /. Gen. Physiol., 1918-19, i, 237. 



^ Pfleiderer, R., Arch. ges. Physiol., 1897, Ixvi, 605. A review of the early- 

 literature is given in this article. 



s Berg, W. N., and Gies, W. J., /. Biol. Chem., 1906-07, ii, 489. 



607 



