yiii] THE PROTEINS AND PROTEASES 121 



Mono-carboxylic di-amiuo acids: 



Arginine or 8-guauidine-a-araino-valeric acid 



NH., 



/ 

 HN=C— NH • CHo • CH. • CH. • CH(NH.,) • COOH 



Lysine or a-6-di-amino-caproic acid 



CH/NH.) • CH2 • CH.2 • CH,. • CH(NH.) • COOH 



Dicarboxylic di-amino acid : 



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

 CH2— S— S— CH.2 



CH(NHo) CH(NH.,) 



I " I " 



COOH COOH 



Aromatic compounds. 

 Mono-carboxylic mono-amino acids : 



Phenyl-alanine or ^-phenyl-a-amino-propionic acid 

 CoHr, •CH2-CH(NH2) -COOH 

 Tyrosine or p-hydroxy-phenyl-alanine 



OH • C6H4 ■ CH. • CH(NH2) • COOH 



Heterocyclic compounds. 

 Proline or a-pyrrolidine-carboxylic acid 



CH, CH, 



r r 



ch, ch-cooh 

 ^nh/ 



Histidine or ia-iminazole-alanine 



CH 



/\ 

 NH N 



I I 



CH=C— CHoCHfNH,) COOH 



Tryptophane or ^-indole-alanine CsH^N • CH, • CH(NH,) • COOH 



-C-CH, •CH(NH,) COOH 

 tv >l CH 



V/^nh/ 



Different proteins are formed b}' various combinations of the above 

 acids and hence give different amounts on hydrolysis. 



There are certain properties and chemical reactions by means of 



