120 



PROTEINS 



COOH 

 I 

 H2N-C— H 



HC = 



I I 



H 



CH2 



I 

 C 



L-Histidine or 

 jS-imidazolealanine 



COOH 



I 

 H2N-C— H 



I 

 CH2 



I 

 CH2 



I 

 CH2 



NH 



I 

 C=NH 



I 

 NH2 



L-Arginine or 

 5-guanidino-a-aminovaleric acid 



COOH 



HjN-C— H 



I 

 CH2 



I 

 CHj 



CH2 



NH, 



COOH 



I 

 H2N— C— H 

 I 

 CH2 



I 

 CHj 



CH2 



NH 

 I 

 C=0 



CH3 



COOH 



L-Ornithine 



IV. Heterocylic amino acids 



COOH 

 I 

 NH2-CH 



NH2 



L-Citrulline 



H 

 HC*^ C- 



CH2 

 I 

 C 



HC^^^C^^^CH 



H H 



L-Tryptophan or 

 indolealanine 



H-C— NH-C— H 



I I 



COOH CH. 



CHa 

 CH2 



NH 

 I 

 C=NH 



I 

 NH2 



L-Octapine 



H,C 



CH, 



HjC^^^^CH-COOH 

 N 

 H 



L-Proline or 

 a-pyrrolidine-carDoxylic acid 



