160 ISOELECTRIC POINTS OF PROTEINS 



Both the compounds of tuberin with acids and with bases were more 

 soluble in the juice than was uncombined tuberin. 



The nature of the slight precipitate that separated when potato 

 juice was made sHghtly alkahne was not determined. 



The Protein in Carrot Juice. — The isoelectric point of the protein 

 in carrot juice coincided with that of tuberin. Remarkably similar 

 also were the properties of carrot juice and the juice of the potato. 

 Existing in nature at nearly the same reaction they combined with 

 acids and bases to nearly the same extent and showed minima in 

 solubihty at the same hydrogen ion concentrations. The greatest 

 difference in behavior concerned the alkaline precipitate which, in 

 the carrot, was nearly as great as the acid precipitate. 



The Protein in Tomato Juice. — The protein of the tomato existed 

 in a precipitated form near its isoelectric point. Accordingly it was 

 not present to any extent in filtered tomato juice. If, however, 

 the considerable acidity at which the tomato exists was neutralized 

 the protein dissolved and was filterable. It then migrated to the 

 anode in an electric field. The addition of sufficient acid to make 

 the hydrogen ion concentration slightly greater than 10~^n again 

 precipitated the protein at its isoelectric point. At greater acidi- 

 ties migration was cathodic. 



