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BOTANICAL 



THE ROLE OF THE ACTIVITY COEFFICIENT OF THE 

 HYDROGEN ION IN THE HYDROLYSIS OF GELATIN. 



By JOHN H. NORTHROP. 



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



(Received for publication, May 9, 1921.) 



/. The Course of the Reaction. 



It is generally assumed that enzymes, and catalysts in general, 

 merely accelerate the velocity of a reaction already taking place. 

 In the case of most enzymes the reaction without the enzyme has 

 been carefully studied and is at least as well known as the enz3ane 

 reaction. The hydrolysis of proteins without the presence of en- 

 . zymes, however, has apparently received very little attention, at 

 least from the standpoint of the kinetics of the reaction. It seemed 

 advisable, therefore, in connection with the study of the proteolytic 

 enzymes to secure some data in regard to the spontaneous hydrolysis, 

 especially since the writer had found that the hydrolysis of gelatin 

 by pepsin^ was very closely connected with the ionization of the 

 protein. It seemed important to determine whether any influence 

 of the ionization could be noticed in the spontaneous reaction. As 

 will be described more fully below, this is found to be the case. 



EXPERIMENTAL. 



Preparation of the Gelatin. — Gelatin was selected as the protein 

 in these experiments since it had already been used in the study of 

 pepsin hydrolysis and also since it does not precipitate in strong 

 acid and alkali. It is also much more accurately titratable by the 

 formol titration than are the other proteins. The gelatin was pre- 

 pared from Cooper's powdered gelatin by washing at the isoelectric 

 point as described by Loeb,^ and was used in a concentration of 



^. 1 Northrop, J. H., /. Gen. Physiol, 1920-21, iii, 211. 

 <>^ 2 L^ei^^ j^ j^ Q^n^ Physiol, 1918-19, i, 237. 



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