Subcellular Metabolite Concentrations

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Abstract
Mitochondrial and cytosolic contents of adenine nucleotides and phosphate were measured in perfused rat livers empolying a technique of fractionation of freeze-fixated tissue in non-aqueous solvents. From the subcellular contents the mitochondrial and cytosolic concentrations of ATP. ADP, AMP and phosphate and the phosphorylation potentials of the subcellular ATP systems were calculated. An attempt was made to elucidate the relationship between mitochnodrial and cytosolic adenine nucleoide systmes and the dependency on the metabolic state of the liver. The following results were obtaines. 1 Under all mtabolic conditions studied the mitochnodrial ATP/ADP ratios were considerably lower than the cytosolic ratios (mitochondria: 0.1–0.7); cytosol: 2–11). 2 The ATP/ADP ratios calculated from overall tissue contents refflect mainly the cytosolic rations. 3 An inverse relationship was found between mitochondrial and cytosilic ATP/ADP ratios, i.e. when the mitchondrial ratios tended to increase, the cytosolic ratios decrease and vice versa. 4 The phosphorylation potentials calculated from the subcellular concertratopms were higher in the cytosol that in the mitochondria. The potential difference varied between 11 and 3 kJ/mol in livers from fed and starved rats, respectively. 5 In the presence of mitochondrial inhibitors, i.e. amytal, dinitrophenol and carboxyatractyloside the potential difference between the subcellular ATP systems decreased predominantly due to an increase in the mitocnodrial ATP/ADP ratios. 6 A correlation between mitochondrial ATP/ADP ratios and the respiratory rates was not obsrved, but the subcellular ratios appeared to correlate with the rate of glycolysi. When the rate of lactate + pyruvate production was increased, the cytosolic ATP/ ADP ratios were increased, too, wheres the mitochondrial ratios tended to decrease. 7 The adenine nucleotides in the cytosol appear to be in near equilibrium catalysed by the adenylate kinase. In the mitochondria, the AMP concentration is much lowe than to be expected under equilibrium conditions. These results were discussed with respect to rate control of processes involved in ATP generation, i.e. Oxidative phosphorylation, adenine nucleotide translocation and glycolysis.