78 PHYSIOLOGY 



CH 3 



I 

 HCNH 2 



I 

 COOH 



is dextro-rotatory, then its stereoisomer 



CH 3 



I 

 H 2 NCH 



I 

 COOH 



will be Isevo-rotatory, and it will be possible to obtain a racemic modification 

 without any influence on polarised light by mixing equal molecules of these 

 two isomeric forms. All the amino-acids derived from proteins are optically 

 active, whereas those obtained 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 disintegration products of 

 protein, is a-<5-diamino-valerianic acid. 



CH 2 NH 2 



I 

 CH 2 



I 

 CH 2 



I 

 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 O 



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 



I 



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 



I 

 COOC 2 H 6 



