vin] THE PROTEINS AND PROTEASES 121 



Mono-carboxylic di-amino acids: 



Arginine or 8-guanidme-a-amiuo-valeric acid 

 NH 2 



HN=C NH CH 2 ' CH 2 CH 2 CH(NH 2 ) COOH 

 Lysine or a-e-di-amino-caproic acid 



CH 2 (NH 2 ) CH 2 CH 2 CH 2 CH(NH 2 ) COOH 



Dicarboxylic di-amino acid : 



Cystine (dicysteine) or di-/3-thio-a-amino-propionic acid 

 CH 2 S S CH 2 



CH(NH 2 ) CH(NH 2 ) 



I I 



COOH COOH ' 



Aro)natic compounds. 

 Mono-carboxylic mono-amino acids : 



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

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

 Tyrosiue or p-hydroxy-phenyl-alanine 



OH C 6 H 4 ' CH 2 CH(NH 2 ) COOH 



Heterocyclic compounds. 



Proline or a-pyrrolidine-carboxylic acid 



CH 2 CH 2 



I ' I 



CH 9 CH-COOH 



Histidine or ^-iminazole-alanine 

 CH 



NH N 



CH=C CH 2 CH(NH 2 ) ' COOH 



Tryptophane or /3-indole-alanine C 8 H 6 N CH 2 CH(NH 2 ) COOH 



-C'CH 2 -CH(NH 2 ) -COOH 



CH 



Different proteins are formed by various combinations of the above 

 acids and hence give different amounts on hydrolysis. 



There are certain properties and chemical reactions by means of 



