200 



UNITY AND DIVERSITY IN BIOCHEMISTRY 



-CHj-CHj-CHj-CO-S-CoA 

 * 



t 

 t 

 I 



♦ 

 -CHa— CO— S— CoA 



CH,~CO-S-CoA 



HS-CoA 



§- ketothiolase 



-CH.-CO-CHi-CO-S- CoA 



elhylencrcducfaie 



-CH,-CH =CH-CO-S-CoA 



- HiO 



H»0 



-CH-CH-CHt-CO-S-CoA 



(5- ketoreductase 



2 H 



DPN ^DPNH 



Fig. 42 (after Lynen) — The enzymatic cycle for the fatty acids. (This process can also be 



considered as a spiral of fatty acids, a Cg fragment being lost or gained at each turn in the 



form of CH3CO — S — CoA. In Fig. 42, the change from one turn of the spiral to the next, 



with addition or subtraction of a C2 fragment, is indicated by the dotted arrow.) 



