PROTEINS. 69 



has not been proven. Most proteins yield relatively small amounts 

 of alanine. 



Serine, C 3 H 7 NO 3 . Serine is a-amino-p-hydroxy-propionic acid 

 and possesses the following structural formula : 



OH NH 2 

 H - C - C - COOH 



A 



FIG. 20. 



SERINE. 



Serine obtained from proteins is Isevo-rotatory, possesses a sweet 

 taste and is quite soluble in water. Serine is not obtained in quantity 

 from most proteins but is yielded abundantly by silk glue. Owing 

 to the difficulty of separating serine it has not been found in a 

 number of proteins in which it probably occurs. Serine crystals are 

 shown in Fig. 20, above. 



Phenylalanine, C 9 H n NO2. This product is phenyl-a-amino- 

 propionic acid, and may be represented graphically as follows : 



NH 2 



I 

 -C-COOH. 



The Isevo-rotatory form is obtained from proteins. Phenylalanine 

 has been obtained from all the proteins examined except from the 



