Activation of Fatty Acid Oxidation by Dihydro- Diphosphopyridine

There are strong indications that oxidative phosphorylation processes are involved in the activation (or “priming, ” “sparking” (1)) of enzymatic fatty acid oxidation (l-5). Two major points of evidence exist: first, it is known that simultaneous oxidation of intermediates of the Krebs tricarboxylic acid cycle under conditions in which oxidative phosphorylation may be observed is required to activate fatty acid oxidation, and, secondly, those substances which are known to uncouple oxidative phosphorylation are also inhibitory to fatty acid oxidation. Among the latter substances are 2,4-dinitrophenol and gramicidin (5), arsenite, methylene blue, brilliant cresyl blue, and others.’ The activation process does not appear to consist simply of a mechanism for generating adenosinetriphosphate (ATP) continuously; ATP alone does not suffice to activate the oxidation. It is presumed that some enzymatic event intermediate in oxidative phosphorylation processes is involved in the priming phenomenon. In preceding papers it has been shown that the oxidation of dihydrodiphosphopyridine nucleotide (DPNH2) causes oxidative phosphorylation (6-9). It became of interest to learn whether the oxidation of DPNHz could also activate fatty acid oxidation under appropriate conditions. Such information would bear on the question of the specific oxidative and phosphorylative processes involved in the activation of fatty acid oxidation, since it is not known whether only the oxidative phosphorylations associated with the cycle are required or whether the additional presence of the cycle intermediates per se is necessary, or whether only the phosphorylations associated with specific oxidative steps are active (such as the step cr-ketoglutarate --j succinate (10)). In this paper experiments are described which demonstrate that the oxidation of DPNHz (in the absence of added Krebs cycle intermediates) does in fact activate fatty acid oxidation in properly supplemented suspen-