BASIC AND ACID PROPERTIES OF PROTEINS 27 



is evident from an examination of numerous preparations of other 

 proteins. All of the vegetable^globulins which have been tested show 

 a distinct acid reaction towards phenolphthalein. Most of them, 

 however, do not permit of determination of the nature of this acidity 

 so readily as does edestin, for, when made neutral to phenolphthalein, 

 many of them are soluble in water. Other proteins besides globulins, 

 such for instance as repeatedly recrystallised ovalbumin and the pro- 

 teins soluble in alcohol, also show the presence of combined acid. 



Erb (no), who studied the acid-binding capacity of edestin, directed 

 his efforts to a determination of the maximum acid-binding power 

 of this protein, and worked with solutions which in all cases contained 

 hydrochloric acid much in excess of that present in the salts just des- 

 cribed. He considers in detail the effect of hydrolytic dissociation of 

 such protein salts on the results obtained in studying their forma- 

 tion. His results indicate the existence of an acid-binding capacity 

 about forty times greater than the quantity of hydrochloric acid re- 

 quired to dissolve edestin. Edestin salts containing such relatively 

 enormous quantities of acid are clearly of a very different order from 

 those which have just been considered and depend on a very high 

 polyacidity of the protein. The equivalent weight of edestin cor- 

 responding to this amount of acid is about 172, whereas that calculated 

 from the acidity of the water-soluble edestin, previously described, is 

 more than 7,000, while from that of the water-insoluble part it is over 

 14,000. 



It is commonly assumed that definite combinations of proteins with 

 acid cannot be obtained under such conditions as to permit of a con- 

 sideration of their molecular relations ; for the proteins are supposed to 

 be extremely weak bases. The basic properties of edestin, however, 

 are so pronounced that it forms much more stable and definite com- 

 pounds with small proportions of acids than do most animal proteins, 

 and consequently conclusions as to its equivalent combining weight 

 deserve more consideration than do those which are based on ex- 

 periments with ovalbumin, or other proteins of animal origin. 



B. Acid Properties. 



It has long been known that the proteins form salts with bases, and 

 numerous attempts have been made to prepare such salts, especially 

 with the heavy metals, with the hope of obtaining evidence of the 

 existence of definite combinations between the protein and the metal. 

 All such attempts, however, have failed to yield definite compounds. 

 Experiments with edestin appear to show that definite salts are formed, 



