53 



Aliphatic Acids and Glycolipides 



the isolation of acetyl coenzyme A (from yeast), the demonstra- 

 tion that the acetyl group was attached to its sulfur atom in a 

 thioester linkage and that acetyl coenzyme A was an active 

 acetylating agent. ^' The enzymic steps in what must be a 

 very general scheme of fatty acid catabolism now can be written 

 as follows:^® 



MgO 

 CoA— SH 



Fatty Acids 

 ATP 



AMP + Pyrophosphate 



DPN® 

 H© +DPNH 



— CH2— CH2— CH2— CO— S— CoA 

 Acyl Coenzyme A 



acy dehydrogenase 



— CH.— CH=CH— CO— S— CoA 

 /rans-a,/3-Dehydroacyl Coenzyme A 



enolhydrase 



— CH2— CH— CH2— CO— S— CoA 



1 

 OH 



I© 



DPN 



©. 



L-/3-Hydroxyacyl Coenzyme A 



H^ + DPNH 



/3-hydroxyacyldehydrogenase 



— CH,— CO— CH2— CO— S— CoA 

 /3-Ketoacyl Coenzyme A 



CoA— SH , 



cleavage enzyme 



— CH2— CO— S— CoA + CH3CO— S— CoA 



At first this process was thought to be reversible or cyclic. It 

 has since been shown that a separate set of enzymes controls 

 fatty acid biosynthesis. The required enzymes and cofactors 

 for the synthetic process have been isolated, and in outline the 



^"^ Feodor Lynen, Ernestine Reichert and Luistraud Rueff , Ann. 574 

 1 (1951). 



^* Feodor Lynen, Ann. Rev. Biochem. 24 653 (1955). 



