THE AMINO ACIDS. 



The amino acids are derivatives of the fatty acids, or of the dibasic 

 acids, in which one or more of the hydrogen atoms in the chain have 

 been replaced by the NH 2 group. They are both amines and acids in 

 their chemical nature. 



These compounds can at the same time contain hydroxyl (OH) 

 groups or thio (SH) groups in their molecule and further aromatic and 

 other radicles can be substituted for hydrogen atoms in the chain. 

 The main characteristic is the presence of an amino group and a car- 

 boxyl group. 



They form an excessively important group of compounds, since 

 they are constituents of the proteins, in which they are combined to- 

 gether in various proportions (see p. 361). Amino acids haveialso been 

 isolated from extracts of animal and vegetable tissues. The following 

 have been definitely identified as constituent's of proteins from which 

 they are obtained by hydrolysis : 



A. Monoaminomonocarboxylic Acids. 



Glycine, or glycocoll, or amino-acetic acid : 



CH 2 (NH 2 ) . COOH. 

 Alanine, or a-aminopropionic acid : 



CH 3 . CH(NH 2 ) . COOH. 

 Serine, or /3-hydroxy-a-aminopropionic acid : 



CH a OH . CH(NH 2 ) . COOH. 



Cysteine, or j8-thio-a-aminopropionic acid, formed by the decom- 

 position of cystine : 



CH 2 SH . CH(NH 2 ) . COOH. 

 Cystine, or dicysteine, or di-(/3-thio-a-aminopropionic acid) :- 



HOOC . CH(NH,) . CH 2 . S S . CH 2 . CH(NH 2 ) . COOH. 

 Phenylalanine, or /3-phenyl-a-aminopropionic acid : 

 C 6 H 5 . CH 2 . CH(NH 2 ) . COOH. 



Tyrosine, or /3-parahydroxyphenyl-a-aminopropionic acid :- 



HO . C e H 4 . CH 2 . CH(NH 2 ) . COOH. 



Histidine, or /3-iminazole-a-aminopropionic acid : 

 CH 



HN N 



CH(NH 2 ).COOH. 



