THE PROTEINS 87 



by synthesis are inactive, and special means have to be devised in order 

 to obtain from the artificially formed racemic amino-acid either the 

 d- or Z-amino-acid. 



If more than one hydrogen atom in an organic acid be replaced 

 by NH 2 we obtain diamino- and triamino-acids. Thus, ornithine, 

 obtained by the splitting up of arginine, one of the commonest dis- 

 integration products of protein, is a- - diamino- valerianic acid. 



CH 2 NH 2 



CH 2 



CH 2 



CH.NH 2 



COOH 



The presence in the amino- acids of the basic radical NH 2 and of 

 the acid group COOH lends to these bodies a double character. In 

 themselves devoid of strong chemical qualities, possessing neither acid 

 nor alkaline reaction, they are able in the presence of strong acids 

 or bases to act either as base or acid. When in solution by themselves 

 it is possible that there is an actual closing of the ring by a soluble union 

 between the NH 2 group and the COOH group, so that, e.g. the formula 

 of glycine may be : 



CH 2 -NH 3 



I I 

 CO 



When such a neutral compound is treated with acid this bond is loosed 

 and we have the salt of the amino-acid. Thus, with hydrochloric 

 acid, glycine forms glycine hydrochlorate : 



CH 2 NH 2 HC1 

 COOH 



a salt which still possesses an acid group and which is therefore capable 

 of combining with ethyl to form the hydrochlorate of the ester of the 

 amino-acid. Thus : 



CH 2 .NH 2 HC1 



COOC 2 H 5 



