EDWIN JOSEPH COHN 701 



Because of their simpler structure, the amino-acids have been found 

 more suitable than the multivalent proteins for the experimental 

 verification of dissociation theory. Accordingly the generalizations, 

 in terms of which we have attempted to explain the dissociation of 

 the proteins, were first worked out for their prototypes, the 

 amino-acids. 



Amino-acids possess at least one amino group, and at least 

 one carboxyl group. The amino groups dissociate as bases and com- 

 bine with acids, much as does ammonia. The carboxyl groups dis- 

 sociate after the manner of organic acids and combine with bases. As 

 a result of its amphoteric nature an amino-acid can form internal 

 salts (20, 21, 22, 23). If the amino group of one acid combines with 

 the carboxyl group of the next with the loss of a molecule of water, 

 a dipeptide is formed which in turn is an amphoteric substance. 

 Polypeptides, in which many amino-acids are combined in this manner, 

 have been synthesized by Emil Fischer (24). They simulate proteins 

 in behavior, and suggest that the free valences in the protein molecule 

 are in all probability derived at least in part from the free groups of 

 the amino-acids. 



The strength of these groups in a number of amino-acids was first 

 determined by Winkelblech (20) in 1901, from the hydrolysis of their 

 acid and basic salts. In the hands of Walker (21), however, Winkel- 

 blech 's data revealed the relations that obtain between the degree of 

 dissociation of an amphoteric electrolyte and its strength as an acid 

 and as a base. Following Walker in the main, therefore, and in part 

 the more recent investigators^ who have amplified his conceptions, 

 we shall deduce the fundamental equations for the dissociation of an 

 amphoteric substance, for our present purposes a protein, P. 



Let HPOH represent the undissociated protein molecule. The 

 protein can dissociate into an hydrogen ion and a protein anion, 



(HPOH) ^ (H+) (POH-) (1) 



and into an hydroxyl ion and a protein cation, 



(HPOH) x± (HP+) (0H-) (2) 



'Notably Hardy (1), Sorensen (13), Lundcn (23), Michaclis (25), Henderson 

 (26), Robertson (27), Pauli (28), and Locb (29). 



