24 CHEMICAL STATICS 



of Osborne and Leavenworth (50) who have shown that edestin 

 combines with, or holds in solution, 34.67 per cent of its weight 

 of copper in the form of cupric hydroxide. This, if we assume 

 that each copper atom unites with one nitrogen atom, involves 

 the union of cupric hydroxide with ten out of every sixteen atoms 

 of nitrogen in the edestin molecule. Now this is exactly the 

 proportion of nitrogen which edestin yields in the form of amino- 

 nitrogen after complete hydrolysis. In other words it is exactly 

 equal to the proportion of — COHN — groups which the unhydro- 

 lysed molecule contains. Precisely similar results were obtained 

 with gliadin. 



To account for the high acid- and base-combining capacity of 

 the proteins we must therefore look, not to the terminal — NH2 

 or — COOH groups, but to the — COHN — groups within the body 

 of the protein molecule. Now two varieties of this union can be 

 conceived, between which it has not proved possible as yet to 

 decide by any direct method of analysis. Thus glycyl-glycin 

 may conceivably be either : 



Keto-form 

 H2N.CH2.CO - HN.CH2.COOH 



or Enol-form 



H2N.CH2.C(OH) = N.CH2.C00H 



and our analytical data, and the modes of decomposition and 

 synthesis of the proteins and peptids do not enable us with any 

 degree of certainty to distinguish between them. Neither form 

 is therefore inconsistent with our present knowledge of the syn- 

 thesis and hydrolysis of proteins and polypeptids, but while 

 the keto-form of the —COHN— group would conceivably possess 

 the power of neutrahzing acids it offers no probable point of union 

 for bases. The enol-form, on the contrary, would provide a 

 point of union for either acids or bases. 



According to Werner's theory of valencies the nitrogen in 

 either of these unions contains two latent valencies, positive and 

 negative, which, while the nitrogen is trivalent, neutralize one 

 another, but which, when the nitrogen becomes pentavalent are 

 capable, respectively, of neutralizing a negative and a positive 

 radical. The enol type of union carries with it the possibility 

 of the following types of reaction : 



