COMPARATIVE HYDROLYSIS OF GELATIN BY PEPSIN, 

 TRYPSIN, ACID, AND ALKALI. 



By JOHN H. NORTHROP. 

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



(Received for publication, June 23, 1921.) 



Gelatin and proteins in general may be hydrolyzed by either acids 

 (hydrogen ions), alkali (hydroxyl ions) pepsin, or trypsin. In all 

 cases the reaction consists in the rupturing of one or more of the 

 peptide linkings with the addition of 1 molecule of water. The ease 

 with which the various linkages are split is very different, as was 

 shown by Fischer,^ in his study of the hydrolysis of the polypeptids. 

 The same phenomenon is shown by the fact that the products of partial 

 hydrolysis of the proteins form a series of increasing complexity — a 

 result of the fact that some of the linkages are much more easily 

 split than others. The same fact is brought out by following the 

 course of " the reaction in strong acid for example. If all the linkages 

 were split at the same rate, the reaction would follow the course of 

 a monomolecular one. This is not the case. The velocity decreases 

 steadily as the reaction proceeds, showing that some of the linkages 

 are split more easily than others. 



The question arises then as to whether those linkages which are 

 most easily split by acid, for instance, are also the most easily split 

 by pepsin and trypsin. There is evidence already that this is not 

 the case. Henriques and Gjaldbak^ have shown by an ingenious 

 modification of the formol titration that protein solutions having the 

 same total content of titratable amino or carboxyl groups but which 

 have been brought to this stage by different hydrolytic agents, may 

 be distinguished from each other by their behavior when titrated 

 with alkali to different end points, showing that, although the total 



^ Fischer, E., Untersuchungen iiber Aminosauren Polypeptide und Proteine. 

 Berlin, 1906. 



« Henriques, V., and Gjaldbak, J. K., Z. physiol. Chem., 1911, kxv, 363; 1913, 

 Ixxxiii, 83. 



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