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Komlodi 2017 Abstract MITOEAGLE Barcelona
Coupling states OXPHOS  + , LEAK  + , ET  +
Enzyme Complex II;succinate dehydrogenase  + , TCA cycle and matrix dehydrogenases  +
Event B3  +
Has abstract [[Image:MITOEAGLE-logo.jpg|left|100px|link
[[Image:MITOEAGLE-logo.jpg|left|100px|link=http://www.mitoglobal.org/index.php/MitoEAGLE|COST Action MitoEAGLE]] Abstract in preparation: Succinate dehydrogenase (SDH or Complex II) is the only enzyme participating both in the [[electron transfer-pathway]] (ET-pathway) and the [[tricarboxylic acid cycle]] (TCA cycle). Succinate is generated by the TCA cycle in the mt-matrix, and cytosolic succinate plays additional metabolic roles, participating in hypoxia-induced cellular reactions and tumorigenesis [1]. Succinate without the Complex I inhibitor rotenone is well known to induce high levels of H<sub>2</sub>O<sub>2</sub> production, which is suggested to be of pathophysiological significance in ischemia-reperfusion injury [2]. The aim of the present study was to investigate the organ- and species-specific regulation of respiration and hydrogen peroxide production in the succinate pathway in view of an ADP-induced respiratory depression observed in some tissues. Experiments were carried out on (i) isolated mitochondria of guinea pig brain, kidney, liver and heart, and (ii) isolated mitochondria or homogenate of mouse cardiac tissue. Mitochondrial respiration was measured by high-resolution respirometry (Oroboros , Innsbruck, Austria). O2k-Fluorometry was applied to the mouse mitochondria for simultaneous measurement of respiration and H<sub>2</sub>O<sub>2</sub> production. In the guinea pig tissues, H<sub>2</sub>O<sub>2</sub> production was measured separately by spectrofluorometry (Photon Technology International, Lawrenceville, NJ). SDH, malic enzyme, phosphoenolpyruvate-carboxykinase (PEPCK) and hydroxy-oxoglutarate aldolase (HOGA) [3] enzyme activities were determined by spectrophotometry (ABL&E-JASCO V-650, Tokyo, Japan) in brain and kidney tissue. In all tissues, H<sub>2</sub>O<sub>2</sub> production was much higher with S(-Rot) than S(+Rot) in the absence of ADP (LEAK state). ADP (2 mM) added to S(+Rot) increased respiration from the LEAK to the OXPHOS state. Surprisingly, however, ADP added to S(-Rot) inhibited oxygen consumption with respect to the LEAK state at low succinate concentration in guinea pig brain and heart, but even at high (10 mM) succinate concentration in mouse heart. This so-called “succinate paradox” was not observed in guine pig liver and kidney. H<sub>2</sub>O<sub>2</sub> production generally declined to low levels after addition of ADP in states S(+Rot) and S(-Rot). The response of NADH to addition of ADP was diametrically different for S(-Rot) (decrease of NADH) and S(+Rot) (increase of NADH) in mouse cardiac tissue. SDH (CII) is inhibited by endogenously produced oxaloacetate (Oa), which is particulaly pronounced in state S(-Rot) [4]. However, exogenously added Oa inhibited SDH measured in brain and kidney, independent of the succinate paradox [5,6]. Addition of rotenone,pyruvate or glutamate abolished the respiration inhibition, because rotenone decreased Oa production and pyruvate or glutamate increased Oa elimination. Addition of malic enzyme to isolated guine pig mitochondria decreased the concentrations of malate and increased the pyruvate concentration, respectively. Measuring HOGA and PEPCK enzyme activity we can draw the conslusion that PEPCK and HOGA activity was higher in kidney than in brain mitochondria. The cause of organ specificity of ADP-mediated inhibition of succinate respiration could be different mechanisms and efficacies of Oa elimination. Our results showed that PEPCK and HOGA enzymes take part in the regulation of OA concentration, which is the main metabolic inhibitor of SDH [6]. Elevated production of H<sub>2</sub>O<sub>2</sub> in the LEAK state can be attributed to succinate-driven reverse electron transfer towards CI which was inhibited by rotenone even at low concentrations of succinate.
e even at low concentrations of succinate.  +
Has editor [[Kandolf G]]  + , [[Komlodi T]]  +
Has title [[File:MITOEAGLE-representation.jpg|left|60px|link=http://www.mitoglobal.org/index.php/MitoEAGLE|COST Action MitoEAGLE]] Succinate dehydrogenase regulation via oxaloacetate in brain mitochondria.  +
Instrument and method Oxygraph-2k  + , O2k-Fluorometer  +
Mammal and model Guinea pig  + , Mouse  +
MiP area Respiration  +
Pathways N  + , S  +
Preparation Isolated mitochondria  + , Homogenate  +
Respiration and regulation ADP  + , mt-Membrane potential  + , Substrate  +
Tissue and cell Nervous system  + , Kidney  + , Heart  + , Liver  +
Was published by MiPNetLab AT Innsbruck Gnaiger E + , AT Innsbruck Oroboros + , HU Budapest Tretter L + , SK Bratislava Sumbalova Z +
Was submitted in year 2017  +
Was submitted to event MitoEAGLE Barcelona 2017 +
Was written by Komlodi T + , Horvath G + , Svab G + , Doerrier C + , Sumbalova Z + , Tretter L + , Gnaiger E +
Categories Abstracts
Modification date
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14:01:49, 23 January 2019  +
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