PROTEINS 71 



acid, is the simplest of the ammo acids which occurs as a protein de- 

 composition product 1 and has the following formula:] 



NH 2 

 H C COOH. 



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 among the first decom- 

 position products of proteins to be discovered. Upon administering 

 benzoic acid to man or lower animals the output of hippuric acid in the 



FIG. 21. GLYCOCOLL ESTER HYDROCHLORIDE. 



urine is greatly increased, thus showing a synthesis from benzoic acid and 

 glycocoll in the organism (see page 619, Chapter XXVIII). Glycocoll, 

 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 decomposition products 

 as the hydrochloride of the ester. The crystalline form of this com- 

 pound is shown in Fig. 21. 



Alanine, CH 3 -CH(NH 2 )-COOH. Alanine is a-amino-propionic acid t 

 and as such it may be represented structurally as follows: 



H NH 2 

 H C C COOH. 



1 1 ; H i 



1 Amino Jorrnic acid (carbamic acid), NH 2 -COOH, is the simplest amino acid. 



