Regulation of the degree of coupling of oxidative phosphorylation in intact rat liver.
The degree of coupling of oxidative phopshorylation q was determined in isolated perfused livers and in livers in vivo from fed and fasted rats. This determination of q was based on a simple nonequilibrium-thermodynamic representation of the major reactions of cytosolic adenine nucleotides, and made use of the measured cytosolic concentrations of adenine nucleotides, phosphate, and lactate/pyruvate ratios in extracted livers. The deviations of the measured values from the theoretically predicted ones at different mass action ratios of the adenylate kinase reaction showed that the basic assumptions of the model, including linearity between flows and thermodynamic forces, were fulfilled in intact liver within the experimental error. The degree of coupling was higher in livers from fed rats than in livers from fasted rats. In particular, the determined values of q were close to the theoretical degrees of coupling qecp and qecf which allow maximization of output power and output flow of oxidative phosphorylation for fed and fasted states, respectively, at optimal efficiency and minimal energy costs. This finding indicates that conductance matching between the load and phosphorylation is fulfilled in vivo. Moreover, it was found that fatty acids lower the degree of coupling in a concentration-dependent manner. This suggested that in livers in the fasted state q is decreased due to elevated fatty-acid levels. Thus fatty acids could act as metabolic regulators of the degree of coupling, enabling the cell to optimize efficiency of oxidative phosphorylation under different metabolic regimes.
D000227:Adenine Nucleotides / Q000378:metabolism*; D000818:Animals; D003593:Cytoplasm / Q000378:metabolism; D004734:Energy Metabolism; D005227:Fatty Acids / Q000502:physiology; D008099:Liver / Q000378:metabolism*; D008297:Male; D008930:Mitochondria, Liver / Q000378:metabolism; D010085:Oxidative Phosphorylation; D051381:Rats; D011919:Rats, Inbred Strains; D013816:Thermodynamics; D014475:Uncoupling Agents
D000227:Adenine Nucleotides; D005227:Fatty Acids; D014475:Uncoupling Agents