title: Threshold effects and control of oxidative phosphorylation in nonsynaptic rat brain mitochondria.
abstract: The amount of control exerted by respiratory chain complexes in isolated nonsynaptic mitochondria prepared from rat brain on the rate of oxygen consumption was assessed using inhibitor titrations. Rotenone, myxothiazol, and KCN were used to titrate the activities of NADH:ubiquinone oxidoreductase (EC 1.6.5.3; complex I), ubiquinol:ferrocytochrome c oxidoreductase (EC 1.10.2.2; complex III), and cytochrome c oxidase (EC 1.9.3.1; complex IV ), respectively. Complexes I, III, and IV shared some of the control of the rate of oxygen consumption in nonsynaptic mitochondria, having flux control coefficients of 0.14, 0.15, and 0.24, respectively. Threshold effects in the control of oxidative phosphorylation were demonstrated for complexes I, III, and IV. It was found that complex I activity could be decreased by approximately 72% before major changes in mitochondrial respiration and ATP synthesis took place. Similarly, complex III and IV activities could be decreased by approximately 70 and 60%, respectively, before major changes in mitochondrial respiration and ATP synthesis occurred. These results indicate that previously observed decreases in respiratory chain complex activities in some neurological disorders need to be reassessed as these decreases might not affect the overall capability of nonsynaptic mitochondria to maintain energy homeostasis unless a certain threshold of decreased complex activity has been reached. Possible implications for synaptic mitochondria and neurodegenerative disorders are also discussed.
authors.affiliation: Department of Neurochemistry, Institute of Neurology, London, England.
authors.forename: G P
authors.initials: GP
authors.lastname: Davey
authors.forename: J B
authors.initials: JB
authors.lastname: Clark
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis; D000818:Animals; D000935:Antifungal Agents / Q000494:pharmacology; D001921:Brain / Q000201:enzymology*; D004579:Electron Transport / Q000502:physiology; D014450:Electron Transport Complex III / Q000187:drug effects / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000187:drug effects / Q000378:metabolism; D004734:Energy Metabolism / Q000502:physiology; D008297:Male; D008452:Maximum Allowable Concentration; D008689:Methacrylates; D008928:Mitochondria / Q000201:enzymology*; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000187:drug effects / Q000378:metabolism; D010085:Oxidative Phosphorylation / Q000187:drug effects*; D010101:Oxygen Consumption / Q000502:physiology; D011190:Potassium Cyanide / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012402:Rotenone / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D017186:Titrimetry
chemical_list: D000935:Antifungal Agents; D008689:Methacrylates; D013844:Thiazoles; D012402:Rotenone; C030517:myxothiazol; D000255:Adenosine Triphosphate; D016660:NAD(P)H Dehydrogenase (Quinone); D003576:Electron Transport Complex IV; D014450:Electron Transport Complex III; D011190:Potassium Cyanide