THE PROTEINS 



19 



On inspection of these formulas it may be estab- 

 lished that certain of the ammo acids are very closely 

 related; thus, glycocoll, the simplest of all, by intro- 

 duction of the group (CH 3 ) becomes alanine. This 

 substance possesses interest because several of the 

 amino acids may be regarded as alanine derivatives. 

 By the replacement of an (OH) group alanine be- 

 comes serine, or by substitution of an (SH) group 

 alanine is changed to cysteine. If the phenyl group 

 (C 6 H 5 ) is introduced phenylalanine is obtained, and 

 the additional substitution of an (OH) group leads to 

 tyrosine. 



CH.NH a 



COOH 



Phenylalanine 



CH a .C 6 H 4 .OH 

 CH.NH a 



COOH 

 Tyrosine 



The introduction of the indole or iminazole group 

 leads to the formation of tryptophane or histidine 

 respectively. 



