THE SYNTHESIS OF THE PROTEINS 3 



protein, is, according to Schiff, given by those substances which contain 

 two CO NH complexes, or two CS NH or C(NH) NH com- 

 plexes, and under certain conditions two CH 2 NH complexes, com- 

 bined together directly, or by a carbon atom, or by a nitrogen atom, e.g., 



CO NH 2 CO NH 2 CO NH 2 CH 2 NH 2 CH 2 NH(CH). 



I I I I I 



CO NH 2 CH 2 NH CO NH., CONH 2 



Oxamide Glycine amide Sarcosine amide 



CO NH 2 CO NH 2 

 Malonamide Biuret 



and also 



CO NH 2 



CH.NH 2 

 CH 2 



CO NH 2 

 Aspartic acid diamide 



give very intense biuret reactions. 

 The presence of 



CH 2 NH 2 



CO NH 



groups in the protein molecule is therefore very probable. Such 

 groups occur when ammo acids, e.g., leucine and glutamic acid, are 

 combined together in the following way : 



CO NH CH CO NH CH CO NH 



C 4 H 9 (CH 2 ) 2 



Leucine 



COOH 



Glutamic acid 



and are repeated when another amino acid is again combined in this 

 manner. 



(c) The combination of amino acids by the formation of CH 2 NH 

 CO groups is also supported by the results obtained in the living body. 

 Hippuric acid C 6 H 5 .CO NH.CH 2 .COOH is formed from benzoic 

 acid and glycine by the kidney, and the bile acids are also combinations 

 of this nature. 



(d) The various results obtained by the condensation together of 

 amino acids, namely, those by Schaal, Grimaux and Curtius, with his 

 biuret base and hippuric acid compounds (see later), many of which give 

 the biuret reaction, support the above supposition, the proof of which 

 has been given by Emil Fischer by his synthesis of the polypeptides 

 where the group CO NH CH 2 occurs repeatedly, and is the 

 chief form of combination in the protein molecule. 



