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"-5B-5BImage:MITOEAGLE-2Dlogo.jpg-7Cleft-7C100px-7Clink=http:-2F-2Fwww.mitoglobal.org-2Findex.php-2FMitoEAGLE-7CCOST-20Action-20MitoEAGLE-5D-5D-20-0AAbstract-20in-20preparation:-0A-0ASuccinate-20dehydrogenase-20(SDH-20or-20Complex-20II)-20is-20the-20only-20enzyme-20participating-20both-20in-20the-20-5B-5Belectron-20transfer-2Dpathway-5D-5D-20(ET-2Dpathway)-20and-20the-20-5B-5Btricarboxylic-20acid-20cycle-5D-5D-20(TCA-20cycle).-20Succinate-20is-20generated-20by-20the-20TCA-20cycle-20in-20the-20mt-2Dmatrix,-20and-20cytosolic-20succinate-20plays-20additional-20metabolic-20roles,-20participating-20in-20hypoxia-2Dinduced-20cellular-20reactions-20and-20tumorigenesis-20-5B1-5D.-20Succinate-20without-20the-20Complex-20I-20inhibitor-20rotenone-20is-20well-20known-20to-20induce-20high-20levels-20of-20H-3Csub-3E2-3C-2Fsub-3EO-3Csub-3E2-3C-2Fsub-3E-20production,-20which-20is-20suggested-20to-20be-20of-20pathophysiological-20significance-20in-20ischemia-2Dreperfusion-20injury-20-5B2-5D.-20The-20aim-20of-20the-20present-20study-20was-20to-20investigate-20the-20organ-2D-20and-20species-2Dspecific-20regulation-20of-20respiration-20and-20hydrogen-20peroxide-20production-20in-20the-20succinate-20pathway-20in-20view-20of-20an-20ADP-2Dinduced-20respiratory-20depression-20observed-20in-20some-20tissues.-20-0A-0AExperiments-20were-20carried-20out-20on-20(i)-20isolated-20mitochondria-20of-20guinea-20pig-20brain,-20kidney,-20liver-20and-20heart,-20and-20(ii)-20isolated-20mitochondria-20or-20homogenate-20of-20mouse-20cardiac-20tissue.-20Mitochondrial-20respiration-20was-20measured-20by-20high-2Dresolution-20respirometry-20(Oroboros-20,-20Innsbruck,-20Austria).-20O2k-2DFluorometry-20was-20applied-20to-20the-20mouse-20mitochondria-20for-20simultaneous-20measurement-20of-20respiration-20and-20H-3Csub-3E2-3C-2Fsub-3EO-3Csub-3E2-3C-2Fsub-3E-20production.-20In-20the-20guinea-20pig-20tissues,-20H-3Csub-3E2-3C-2Fsub-3EO-3Csub-3E2-3C-2Fsub-3E-20production-20was-20measured-20separately-20by-20spectrofluorometry-20(Photon-20Technology-20International,-20Lawrenceville,-20NJ).-20SDH,-20malic-20enzyme,-20phosphoenolpyruvate-2Dcarboxykinase-20(PEPCK)-20and-20hydroxy-2Doxoglutarate-20aldolase-20(HOGA)-20-5B3-5D-20enzyme-20activities-20were-20determined-20by-20spectrophotometry-20(ABL-26E-2DJASCO-20V-2D650,-20Tokyo,-20Japan)-20in-20brain-20and-20kidney-20tissue.-0A-0AIn-20all-20tissues,-20H-3Csub-3E2-3C-2Fsub-3EO-3Csub-3E2-3C-2Fsub-3E-20production-20was-20much-20higher-20with-20S(-2DRot)-20than-20S(+Rot)-20in-20the-20absence-20of-20ADP-20(LEAK-20state).-20ADP-20(2-20mM)-20added-20to-20S(+Rot)-20increased-20respiration-20from-20the-20LEAK-20to-20the-20OXPHOS-20state.-20Surprisingly,-20however,-20ADP-20added-20to-20S(-2DRot)-20inhibited-20oxygen-20consumption-20with-20respect-20to-20the-20LEAK-20state-20at-20low-20succinate-20concentration-20in-20guinea-20pig-20brain-20and-20heart,-20but-20even-20at-20high-20(10-20mM)-20succinate-20concentration-20in-20mouse-20heart.-20This-20so-2Dcalled-20“succinate-20paradox”-20was-20not-20observed-20in-20guine-20pig-20liver-20and-20kidney.-20H-3Csub-3E2-3C-2Fsub-3EO-3Csub-3E2-3C-2Fsub-3E-20production-20generally-20declined-20to-20low-20levels-20after-20addition-20of-20ADP-20in-20states-20S(+Rot)-20and-20S(-2DRot).-20The-20response-20of-20NADH-20to-20addition-20of-20ADP-20was-20diametrically-20different-20for-20S(-2DRot)-20(decrease-20of-20NADH)-20and-20S(+Rot)-20(increase-20of-20NADH)-20in-20mouse-20cardiac-20tissue.-20-0A-0ASDH-20(CII)-20is-20inhibited-20by-20endogenously-20produced-20oxaloacetate-20(Oa),-20which-20is-20particulaly-20pronounced-20in-20state-20S(-2DRot)-20-5B4-5D.-20However,-20exogenously-20added-20Oa-20inhibited-20SDH-20measured-20in-20brain-20and-20kidney,-20independent-20of-20the-20succinate-20paradox-20-5B5,6-5D.-20Addition-20of-20rotenone,pyruvate-20or-20glutamate-20abolished-20the-20respiration-20inhibition,-20because-20rotenone-20decreased-20Oa-20production-20and-20pyruvate-20or-20glutamate-20increased-20Oa-20elimination.-20Addition-20of-20malic-20enzyme-20to-20isolated-20guine-20pig-20mitochondria-20decreased-20the-20concentrations-20of-20malate-20and-20increased-20the-20pyruvate-20concentration,-20respectively.-20Measuring-20HOGA-20and-20PEPCK-20enzyme-20activity-20we-20can-20draw-20the-20conslusion-20that-20PEPCK-20and-20HOGA-20activity-20was-20higher-20in-20kidney-20than-20in-20brain-20mitochondria.-0A-0AThe-20cause-20of-20organ-20specificity-20of-20ADP-2Dmediated-20inhibition-20of-20succinate-20respiration-20could-20be-20different-20mechanisms-20and-20efficacies-20of-20Oa-20elimination.-20Our-20results-20showed-20that-20PEPCK-20and-20HOGA-20enzymes-20take-20part-20in-20the-20regulation-20of-20OA-20concentration,-20which-20is-20the-20main-20metabolic-20inhibitor-20of-20SDH-20-5B6-5D.-20Elevated-20production-20of-20H-3Csub-3E2-3C-2Fsub-3EO-3Csub-3E2-3C-2Fsub-3E-20in-20the-20LEAK-20state-20can-20be-20attributed-20to-20succinate-2Ddriven-20reverse-20electron-20transfer-20towards-20CI-20which-20was-20inhibited-20by-20rotenone-20even-20at-20low-20concentrations-20of-20succinate." 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