The control of tricarboxylate-cycle oxidations in blowfly flight muscle. The steady-state concentrations of citrate, isocitrate 2-oxoglutarate and malate in flight muscle and isolated mitochondria.
1. Blowfly (Phormia regina) flight-muscle mitochondria were allowed to oxidize pyruvate under a variety of experimental conditions, and determinations of the citrate, isocitrate, 2-oxoglutarate and malate contents of both the mitochondria and the incubation medium were made. For each intermediate a substantial portion of the total was present within the mitochondria. 2. Activation of respiration by either ADP or uncoupling agent resulted in a decreased content of citrate and isocitrate and an increased content of 2-oxoglutarate and malate when the substrate was pyruvate, APT and HCO3 minus. Such a decrease in citrate content was obscured when the substrate was pyruvate and proline owing to a large rise in the total content of tricarboxylate-cycle intermediates in the presence of proline and ADP. 3. An experiment involving oligomycin and uncoupling agent demonstrated that the ATP/ADP ratio is the main determinant of flux through the tricarboxylate cycle, with the redox state of nicotinamide nucleotide being of lesser importance. 4. Addition of ADP and Ca-2+ to activate the oxidation of both glycerol 3-phosphate and pyruvate, simulating conditions on initiation of flight, gave a decrease in citrate and isocitrate and an increase in 2-oxoglutarate and malate content. 5. There was a good correlation between these results with isolated flight-muscle mitochondria and the changes found in fly thoraces after 30s and 2 mihorax. 6. It is concluded that NAD-isocitrate dehydrogenase (EC 1.1.1.41) controls the rate of pyruvate oxidation in both resting fly flight muscle in vivo and isolated mitochondria in state 4 (nomenclature of Change & Williams, 1955).
D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002951:Citrates / Q000378:metabolism; D002952:Citric Acid Cycle; D004175:Diptera / Q000378:metabolism; D005994:Glycerophosphates / Q000378:metabolism; D007521:Isocitrate Dehydrogenase / Q000378:metabolism; D007523:Isocitrates / Q000378:metabolism; D007656:Ketoglutaric Acids / Q000378:metabolism; D008293:Malates / Q000378:metabolism; D008931:Mitochondria, Muscle / Q000032:analysis / Q000187:drug effects / Q000378:metabolism; D009132:Muscles / Q000378:metabolism*; D009840:Oligomycins / Q000494:pharmacology; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D011773:Pyruvates / Q000378:metabolism; D014475:Uncoupling Agents / Q000494:pharmacology
D002951:Citrates; D005994:Glycerophosphates; D007523:Isocitrates; D007656:Ketoglutaric Acids; D008293:Malates; D009840:Oligomycins; D011773:Pyruvates; D014475:Uncoupling Agents; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D007521:Isocitrate Dehydrogenase