68 



PHYSIOLOGICAL CHEMISTRY. 



Glycocoll, as the formula shows, contains no asymmetric carbon atom, 

 and is the only amino acid yielded by protein decomposition which 

 is optically inactive. Glycocoll and leucine were the first decom- 

 position products of proteins to be discovered (1820). Upon ad- 

 ministering benzoic acid to animals the output of hippuric acid 

 in the urine is greatly increased, thus showing a synthesis of benzoic 

 acid and glycocoll in the organism (see p. 160, Chapter IX). Glyco- 

 coll, ingested in small amount, is excreted in the urine as urea, 

 whereas if administered in excess it appears in part unchanged in 

 the urine. It is usually separated from the mixture of protein de- 

 composition products as the hydrochloride of the ester. The crys- 

 talline form of this compound is shown in Fig. 19. 



FIG. 19. 



GLYCOCOLL ESTER HYDROCHLORIDE. 



Alanine, C 3 H 7 NO 2 . Alanine is a-amino-propionic acid, and as 

 such it may be represented structurally as follows : 



H NH 2 

 H-C-C-COOH. 



ili 



Obtained from protein substances, alanine is dextro-rotatory, is 

 very soluble in water, and possesses a sweet taste. Tyrosine, 

 phenylalanine, cystine and serine are derivatives of alanine. This 

 amino acid has been obtained from nearly all proteins examined. 

 Its absence, from those proteins from which it has not been obtained. 



