Regulation of the Metabolism of Rabbit Liver Mitochondria by Long Chain Fatty Acids and Other Uncouplers of Oxidative Phosphorylation

Abstract

Abstract 1. Oleate, 2,4-dinitrophenol, and other uncouplers of oxidative phosphorylation have been compared with respect to their ability to stimulate the production of phosphoenolpyruvate from citric acid cycle intermediates and to alter the pathways of oxidation of pyruvate, glutamate, glutamine, and proline by rabbit liver mitochondria. 2. Oleate or 2,4-dinitrophenol stimulated the production of phosphoenolpyruvate from citrate or α-ketoglutarate even at concentrations of uncouplers which completely block respiratory chain-linked oxidative phosphorylation. 3. With malate or oxalacetate as substrate, uncouplers stimulated respiration and formation of phosphoenolpyruvate. In the presence of arsenite, production of phosphoenolpyruvate was blocked and pyruvate accumulated from these substrates. Added ATP restored phosphoenolpyruvate formation. 4. With pyruvate as substrate, low levels of uncouplers stimulated respiration, formation of citric acid cycle intermediates, and phosphoenolpyruvate. As the concentrations of uncouplers were increased, net formation of citrate, malate, and phosphoenolpyruvate was abolished, and pyruvate was diverted to acetoacetate. The level of added inorganic phosphate markedly influenced the rate of carboxylation of pyruvate. 5. With glutamate, glutamine, or proline as substrate, relatively low levels of oleate or 2,4-dinitrophenol gave optimal stimulation of respiration. However, at higher concentrations of uncouplers, formation of phosphoenolpyruvate was further increased without alteration of the respiratory rate. These effects may be explained by alterations in the relative rates of glutamic dehydrogenase and glutamicoxalacetic transaminase, the oxidation-reduction state of NAD(P), and the steady state level of oxalacetate. 6. The accumulated evidence supports the view that increased hepatic free fatty acids may facilitate gluconeogenesis in rabbit liver by uncoupling mitochondrial respiration.