TRKILYCERIDES AND PATTY ACIDS 105 



quantitative conversion of pj^-iivate to CO.. and H2O via the tricarboxylic 

 acid cycle. In a subsequent study, Grafflin and Green ^"^ reported the com- 

 plete oxidation of a series of saturated straight-chain acids, of some jS- 

 hydroxy- and /3-keto-acids, and also of some misaturated acids, by cyclo- 

 phorase, in the presence of intermediates of the tricarboxylic acid cycle. 

 On the other hand, certain a- and jS-substituted acids were not attacked; 

 7-phenyl acids were found to be inhibitors of fatty acid oxidation, although 

 they were slowly oxidized by the cyclophorase system. 



Lehninger^ is of the opinion that the differences between his oxidase sys- 

 tem and the cyclophorase system are only superficial, and are related to the 

 different conditions under which the studies were carried out. One varia- 

 tion is the yield of acetoacetate, which is much lower in the cyclophorase 

 preparation than in that of Lehninger. This results from the larger pro- 

 portion of fatty acid which is completely oxidized in the former case as the 

 result of the presence of a greater amount of tricarboxylic acid intermedi- 

 ates. In addition, cyclophorase is more sensitive to malonate than is the 

 Lehninger preparation. Lehninger^ states that this sensitivity is related 

 not only to the proportion of fatty acid passing through the tricarboxylic 

 acid cycle, but also to the "sparking"phenomenon. The older the prepara- 

 tion, the more "sparker" is required, and the greater the capacity of malo- 

 nate to effect an inhibition. Knox and associates'^* and Grafflin and Green'"* 

 reported that the "sparking" phenomenon could be brought about anaero- 

 bically by use of ferricyanide as a hydrogen acceptor. 



(c) Fatty Acid Oxidase of Drysdale and Lardy. Drysdale and Lardy '^^ 

 described an enzyme system which oxidized fatty acids in the presence of an 

 artificial electron acceptor. The enzyme system was prepared by the ex- 

 traction of an acetone-dried powder of rat liver mitochondria with water. 

 The extract consists of soluble proteins which are not sedimented when cen- 

 trifuged at 120,000 X g. for three hours. ATP is required for activation; 

 one mole of ATP permits the oxidation of one mole of fatty acid. CoA is 

 likewise needed, in addition to ATP. When fatty acids labeled with C'* 

 in the carboxyl group were oxidized with this enzyme system, the resulting 

 acetoacetate was found to be labeled on both the carboxyl and the carbonyl 

 groups. This fact indicates that the oxidase functions by splitting off two- 

 carbon fragments from the fatty acids; they are then recombined to yield 

 acetoacetate. When oxaloacetate is present, the fatty acids are quantita- 

 tively converted to citrate. 



168 W. E. Knox, B. N. Noyce, and V. H. Auerbach, /. Biol. Chem., 176, 117-122 (1948). 

 1" G. R. Drysdale and H. A. Lardy, /. Biol. Chem., 202, 119-136 (1953). 



