JOHN H. NORTHROP 71 



Action of Trypsin on Gelatin previously Hydrolyzed by Acid. 



The results of this experiment are shown in Fig. 8, and Table V. 

 The course of the acid hydrolysis is quite different from that due to 

 the trypsin since the addition of trypsin to the hydrolyzed gelatin 

 is able to cause a still further increase even after the total number of 

 linkages already split by the acid is greater than that which could 

 be split by trypsin alone. 



SUMMARY. 



A comparison has been made of the relative velocity of hydrolysis 

 of the various peptid linkings of the gelatin molecule when hydrolyzed 

 by acid, alkali, pepsin or trypsin. It has been found that : 



1 . Those linkages which are most rapidly split by pepsin or trypsin 

 are among the more resistant to acid hydrolysis. 



2. Those linkages which are hydrolyzed by pepsin are also hydro- 

 lyzed by trypsin. 



3. Trypsin hydrolyzes linkages which are not attacked by pepsin. 



4. Of the linkages which are hydrolyzed by both enzymes, those 

 which are most rapidly hydrolyzed by pepsin are only slowly attacked 

 by trypsin. fm 



:>. Those Imkages^ which are attacked by trypsm or pepsin are 

 among the ones first (most rapidly) hydrolyzed by alkali. 



In general it may be said that the course of the early stages of 

 hydrolysis of gelatin is similar with alkali, trypsin, or pepsin and quite 

 different with acid. 



