Mono-carboxylic 

 di-amino acids. 



Dicarboxylic 

 di-amino acid. 



' Ornithine or o-8-di-amino-valeric acid 



NH 2 CH 2 CH 2 CH 2 CHNH 2 COOH 

 Arginine or 5-guanidine a-araino-valeric acid 



/NH 8 

 HN=C 



\NH CH 2 CH 2 CH 3 CHNH 2 COOH 

 Lysine or a--di-amino-caproic acid 



NH 2 CH 2 CH 2 CH 2 CH 2 CHNH 2 COOH 

 I Di-amino-trihydroxy-dodecanic acid * C^HogOjNjj 

 Cystine or di [0-thio o-amino propionic] acid 

 CH 3 -S S CH 2 



CHNH 2 

 COOH 



CHNH 2 

 COOH 



(2) Aromatic Compounds. 



(Phenyl alanine or /3-phenyl a-amino propionic acid 

 C 8 H 8 CH 2 CHNH 2 COOH 

 Tyrosine or 0-parahydroxyphenyl o-amino-propionic acid 

 HOC 6 H,CH 2 CHNH 2 COOH 



(3) Heterocydic Compounds. 



CH 2 CH 2 



Proline or a-pyrrolidine carboxylic acid CH 2 CHCOOH 



NH 



Hydroxyproline or hydroxy o-pyrrolidine carboxylic acid 

 Histidine or /3-imidazol a-amino propionic acid 

 CH= C CH 2 CHNH 2 COOH 



N NH 



V 



CH 



Tryptophane /3-indole a-amino propionic acid 

 C CH 2 CHNH 2 COOH 



XX 



C 6 H 4 



CH 



NH 



.The above list comprises most of the more important 

 cleavage products of proteins, the constitution of which has 

 been definitely established. 



Since different proteins give rise to different amounts of 

 these various substances, it is obvious that a careful quantita- 

 tive determination of the amounts of these acids produced by 

 the hydrolysis of different proteins must be of considerable 

 value. 



' The constitutional formula of this substance has not yet been determined 



