PROTEINS 



117 



B. Acids in'th aromatic nuclei: 



COOH 

 I 

 H2N-C-H 

 I 



I 



HC^ CH 



I II 



H 



L-Phenylalanine 



COOH 

 I 

 H2N— C— II 

 I 



CH2 

 I 



I II 



1 

 OH 



L-Tyrosine or 

 p-hydroxyphenylalanine 



C. Acids containing sulfur: 

 COOH 



HjN-C— H 



CH2 

 I 

 SH 



L-Cysteine or 

 ^-thiolalanine 



COOH 

 I 

 H,N— C— H 



CH2 



\ 



S 

 I 



s 



I 



CH2 



1 



H— C— NH2 



I 

 COOH 



L-Cystine (dicysteine) or 

 di-/3-thiolalanme 



COOH 



I 

 H2N-C— H 



I 

 CH2 



I 

 S 



I 

 CH2 



I 

 H-C— NH2 



I 

 COOH 



L-Lanthionine 



COOH 

 I 

 H2N-C-H 



CH2 



I 

 CH2 



I 



s 



I 



CH3 



L-Methionine or 

 a-amino-7-methylthiol- 

 butyric acid 



COOH 

 I 

 H2N— C— H 



CH2 

 I 



CH2 

 I 

 SH 



L- Homocysteine 



COOH COOH 

 I I 



H2N— C— H H2N— C— H 



CH2 CH2 



I I 



CH2 CHi 



I I 



s s 



L-Homocystine 

 (dihomocysteine) 



