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Starkov AA, Fiskum G, Chinopoulos C, Lorenzo BJ, Browne SE, Patel MS, Beal MF: Mitochondrial alpha-ketoglutarate dehydrogenase complex generates reactive oxygen species. J Neurosci. 2004 Sep 8;24(36):7779-88.
Mitochondria-produced reactive oxygen species (ROS) are thought to contribute to cell death caused by a multitude of pathological conditions. The molecular sites of mitochondrial ROS production are not well established but are generally thought to be located in complex I and complex III of the electron transport chain. We measured H (2) O (2) production, respiration, and NADPH reduction level in rat brain mitochondria oxidizing a variety of respiratory substrates. Under conditions of maximum respiration induced with either ADP or carbonyl cyanide p-trifluoromethoxyphenylhydrazone,alpha-ketoglutarate supported the highest rate of H (2) O (2) production. In the absence of ADP or in the presence of rotenone, H (2) O (2) production rates correlated with the reduction level of mitochondrial NADPH with various substrates, with the exception of alpha-ketoglutarate. Isolated mitochondrial alpha-ketoglutarate dehydrogenase (KGDHC) and pyruvate dehydrogenase (PDHC) complexes produced superoxide and H (2) O (2). NAD (+) inhibited ROS production by the isolated enzymes and by permeabilized mitochondria. We also measured H (2) O (2) production by brain mitochondria isolated from heterozygous knock-out mice deficient in dihydrolipoyl dehydrogenase (Dld). Although this enzyme is a part of both KGDHC and PDHC, there was greater impairment of KGDHC activity in Dld-deficient mitochondria. These mitochondria also produced significantly less H (2) O (2) than mitochondria isolated from their littermate wild-type mice. The data strongly indicate that KGDHC is a primary site of ROS production in normally functioning mitochondria. |
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