THE ACTION OF RENNIN ON CASEIN*f 



ALFRED W. BOSWORTH. 



SUMMARY. 



A solution of calcium caseinate neutral to litmus and free from 

 all other salts is not curdled by rennin. 



A solution of calcium caseinate acid to litmus, which contains two 

 equivalents of base for each molecule of casein, is curdled by rennin. 



Solutions of ammonium, sodium or potassium caseinates are not 

 curdled by rennin. In such solution, however, the casein is changed 

 to paracasein, the paracaseinates of these bases being soluble. 



When paracasein is produced from casein by the action of rennin 

 no other substance is formed. Two molecules of paracasein are 

 produced from each molecule of casein as a result of this action. 



Rennin is not, strictly speaking, a coagulating ferment; the coag- 

 ulation being a secondary effect, the result of a change in solubilities. 



Rennin action is probably a hydrolytic cleavage and may be 

 considered the first step in the proteolysis of casein. It would 

 follow from this that the action now attributed to rennin may be 

 produced by any proteolytic enzyme. Work along this line is being 

 carried out by the author. 



In the light of the results reported in this paper together with 

 those of Van Slyke and Bosworth the retarding action of soluble 

 salts of ammonium, sodium and potassium on the coagulation of 

 milk or casein solutions by rennin may be explained as follows: 

 The addition of salts of these bases to milk or casein solutions 

 results in a double decomposition whereby the calcium caseinate 

 is changed to a caseinate of the base added. These are converted 

 to paracaseinates by rennin, but owing to the fact that all the para- 

 caseinates of these bases are soluble, no coagulation results. 



INTRODUCTION. 



The changes produced by the action of rennin in milk and solu- 

 tions of casein have been the subject of many investigations. Fremy 1 

 was probably the first to give an explanation of this phenomenon. 

 He believed the power to coagulate milk possessed by an extract 

 of the mucous lining of a calf's stomach to be due to the presence 



* Also printed in Jour. Biol. Chem., 15:231-236, as a contribution "From the 

 Biochemical Laboratory of the Harvard Medical School, Boston, and the Chemical 

 Laboratory of the New York Agricultural Experiment Station, Geneva, N. Y." 



t Reprint of Technical Bulletin No. 31, September, 1913. 



1 Fremy: Ann. de pharm. (Liebig), 31: 188, 1839. 



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