CONSEQUENCES OF THE POLYPEPTID STRUCTURE 23 



and the regular decomposition of the proteins into their con- 

 stituent amino-acids, upon hydrolysis, would be unintelligible 

 (30). Moreover, in the synthetical polypeptids, which closely 

 resemble the natural peptones in their behavior, the linkage of 

 the amino-acids is not radial but catenary in character * and 

 the peptids which have been isolated from the mixed products 

 of partial protein hydrolysis are likewise catenary in structure. 



In the second place, as Vernon has pointed out (72), although 

 the power of the sum of the decomposition-products of a protein 

 to neutralize bases is greater, yet it is only very slightly greater 

 than that of the unhydrolysed protein. Now in the process of 

 hydrolysis the — COHN— groups of the protein are split into 

 — NH2 and — COOH groups; yet this results in no pronounced 

 gain of combining-capacity for bases. The obvious conclusion is 

 that the —COHN— group within the protein molecule must be 

 nearly as efficient in accomplishing the neutralization of bases 

 as. the —COOH group of the constituent amino-acids out of 

 which the protein is built up. 



Direct proof, however, that terminal — NHo groups are not 

 responsible for any appreciable proportion of the acid-combining 

 capacity of proteins has been furnished by the recent experiments 

 of Blasel and Matula (5) and Pauli and Hirschfeld (51). These 

 investigators prepared deaminized gelatin by acting upon gelatin 

 with nitrous acid, thus destroying all the free — NH2 groups in 

 the molecule. They then compared, with the aid of the gas- 

 chain, the acid-combining capacity of the deaminized gelatin 

 with that of normal gelatin. They found that the combining- 

 capacity of deaminized gelatin for acids is but slightly inferior 

 to that of ordinary gelatin, indicating, beyond any question, that 

 the combining-capacity of gelatin for acids is, in very large pro- 

 portion, attributable to elements of the molecule other than 

 free — NH2 groups. The inference is unavoidable that the ele- 

 ments of the molecule which actually participate in the union 

 with acids are, in very large proportion, the —COHN— groups 

 within the body of the protein molecule. 



Very strong evidence that the same structural elements of the 

 protein molecule are responsible for the neutralization of bases 

 by proteins has also been recently afforded by the investigations 



* Even when dicarboxylic acids enter into the compounds, Cf . Fischer and 

 Koenigs (24), and Fischer and Schmidhn (26). 



