TRIGLYCERIDES AND FATTY ACIDS 109 



hydrogenase is an enzyme which catalyzes the reversible oxidative phos- 

 phorylation of acetaldehyde to acetylphosphate. Inorganic phosphate and 

 diphosphopyridine nucleotide (DPN) participate in the reaction. Aldehyde 

 is also oxidized in the absence of phosphate or arsenate. The same en- 

 zyme is capable of producing oxidative phosphorylative of propionaldehyde 

 and of butyraldehyde. 



(h) ^-HydroxyhiUyrate Dehydrogenase System. Lehninger and Greville^^* 

 have sho^\^l that L-;5-hydroxybutyrate causes the reduction of DPN, pre- 

 sumably by the already kno^vn^^'' L-specific DPN-linked (3-hydroxybutyric 

 dehydrogenase which does not attack the Z)-isomer. ^^* The Z)-isomer also 

 causes reduction of DPN, but only if the extracts are supplemented with 

 ATP, CoA, and Mg. Under these conditions, the Z)-/3-hydroxybutyrate 

 was shown to be capable of forming a CoA derivative at the expense of ATP. 

 It is suggested that a dehydrogenase, specific for the Z)-isomer, reversibly 

 catalyzes the reduction of Z)-/S-hydroxybutyrate CoA, with the formation 

 of acetoacetyl CoA. 



(i) General Considerations in Fatty Acid Oxidase Systems. The most im- 

 portant fact is the universality of action of the oxidase systems. Thus, Ken- 

 nedy and Lehninger reported that all of the saturated straight-chain acids 

 from butyrate to stearate were oxidized by isolated mitochondria. ^" Cyclo- 

 phorase was found to be inactive A\^th acids having more than thirteen 

 carbons.* This is probably to be ascribed to the technical difficulties of 

 preparing suitable emulsions of these higher fatty acids at a pH of 7.4. 



The fatty acid oxidases also oxidize the misaturated acids. Thus, Ken- 

 nedy and Lehninger^'^^ showed that oleic, linoleic, linolenic, and vaccenic 

 acids are all readily oxidized; priming is required in all cases. Autoxida- 

 tion, however, is only a negligible factor. It is remarkable that even the un- 

 natural trans isomer of oleic acid, elaidic acid, is as rapidly oxidized as is 

 oleic acid.^" Grafflin and Green ^"^ reported that both cis and trans forms of 

 crotonic acid and /3, 7-unsaturated acids are oxidized by cyclophorase. 



In order that the oxidase system may function, it is necessary that the 

 substrate have a free carboxyl group. Thus, long-chain fatty alcohols, al- 

 dehydes, amides, and N-acylglycine derivatives are not oxidized. Although 

 fatty acid esters and phospholipids are oxidized, it seems probable that 

 oxidation occurs only after hydrolysis of the ester linkage, smce fat oxidase 

 systems contain esterases. However, when the substrate contains two car- 



1" A. L. Lehninger and G. D. Greville, Biochim. ei Biophys. Acta, 12, 188-202 (1953). 

 "« D. E. Green, J. G. Dewar, and L. F. Leloir, Biochem. J., 31, 934-949 (1937). 

 1" E. P. Kennedy and A. L. Lehninger, J. Biol. Chem., 185, 275-285 (1950). 



