604 



METABOLISM 



Two cysteine molecules united at the "S" groups give cyst inc. 



CH..S - cir 



NH 



COOH 



NH 



3. Phenylalanine has a C^ (phenyl) group, CH 2 C 6 H 5 -CH 



NH 2 



4. Tyrosine has a C 6 H 4 OH (phenol) group, CH 2 C 6 H 4 OH - CH 



\ 



COOH 



/ \ 

 5. Tryptophane has a C 6 H 4 CH (indole) group: 



\ / 

 NH 



C 6 H/ CH 



\ / 

 NH 



CH 



/ \ 

 N NH 



6. Histidine has a 



CH C - (imi 



(imidazole) group: 



CH 





H 



I ! 



CH = C.CH, . CH. NH,-COOH. 



The last two are also called Ueterocyclic compounds, of which there 

 is another, viz.; 



Proline (and oxyproline), which is a-pyrrolidine carboxylic acid: 



CH 2 CH 2 



I 



CH, CH.COOH 



\ / 

 NH 



Other amino acids are: 



(1) Valine 

 Leucine 

 Isoleucine 

 thus: 



CH 



I 



CH.NH 2 



I 

 COOH 



\ 



CH, CH, CH :1 CH 3 CH, C 2 H 5 



CH 



CH.NH 2 

 COOH 

 (valine) COOH (isoleucine) 



CH 



! 



CH 2 



I 

 CH.NH., 



COOH 



(leucine) 



