108 III. OXIDATION AND METABOLISM 



from beef liver mitochondria. It is believed that the enzyme acts by the 

 formation of E Ac~ (acetate enzyme) as an intermediary complex. 



As soon as acetoacetyl-CoA is formed, the reaction may be terminated in 

 either of the following ways :^®^ 



1. By enzymatic deacylation of acetoacetyl-CoA to acetoacetate. 



2. By cleavage of acetoacetyl-CoA to two molecules of acetyl-CoA, fol- 

 lowed by their condensation with oxaloacetate. 



Thus, according to reaction 1, acetoacetate will be the end-product of 

 fatty acid oxidation while, according to reaction 2, citrate is formed, and 

 the acid may become completely oxidized to CO2 and H2O. 



(/) Acetate-Activating Enzyme. Hele^^^ prepared an acetate-activating 

 enzyme (AAE) from beef heart mitochondria. The partially purified en- 

 zyme was believed to be associated with a single protem. AAE was found 

 to be very unstable under the conditions of electrophoresis ; at higher pu- 

 rity levels, it was fomid to undergo inactivation after dialysis. Beinert and 

 associates'^" also reported the isolation of an enzyme system from pig and 

 rabbit heart which catalyzes the reversible conversion of acetate and CoA to 

 acetyl CoA, and the simultaneous change of ATP to AMP and inorganic 

 pyrophosphate. Millerd and Bonner'™ described a similar AAE system 

 from the plant kingdom, in this case from spinach. This system may be 

 associated with mitochondria; it has been demonstrated in all plant tissues 

 which have been investigated. The AAE from plants was found to be ac- 

 tive with a variety of normal and branched-chain fatty acids, in addition to 

 acetate. Acetoacetate was also formed by the plant acetoacetate cleavage 

 enzyme. 



{g) Aldehyde Dehydrogenase Enzyme. The association of the oxidation 

 of the fatty acid aldehydes with that of the fatty acids can be predicated by 

 the demonstration that the appropriate enzyme system occurs in nature. 

 Burton and Stadtman'^^ prepared a purified aldehyde dehydrogenase from 

 the anaerobe, Clostridium kluyveri which catalyzes the DPN-linked oxida- 

 tion of acetaldehyde in the presence of CoA to acetyl CoA. This aldehyde 

 dehydrogenase was also shown to effect the oxidation of propionaldehyde, 

 butyraldehyde, and glycolaldehyde to the corresponding acyl CoA deriva- 

 tive. 



According to Harting and Velick,'^^ glyceraldehyde-3-phosphate de- 



"« H. Beinert, D. E. Green, P. Hele, H. Hift, R. W. von Korff, and C. V. Rama- 

 krishnan, J. Biol. Chem., 203, 35-45 (1953). 



1" R. M. Burton and E. R. Stadtman, J. Biol. Chem., 202, 873-890 (1953). 

 "* J. Harting and S. F. Velick, J. Biol. Chem., 207, 857-865 (1954). 



