MiP2005: Session 7

Mitochondrial Physiology Network 10.9: 84 (2005) - download pdf

 

ROS generation by mitochondrial respiratory chain - implication for neurodegenerative diseases.

AP Kudin, Wolfram S Kunz

Dept. Epileptology, University Bonn, Medical Center, Sigmund-Freud-Str. 25, D-53105 Bonn, Germany. - wolfram.kunz@ukb.uni-bonn.de

    We have quantified the superoxide and H2O2 production rates of intact rat brain and skeletal muscle mitochondria under condition of oxygen saturation using p-hydroxyphenylacetate and Amplex red as fluorescent probes for H2O2 generation and hydroethidine as probe for superoxide formation. The localisation of superoxide producing sites was determined by evaluating the effects of SOD addition. In accordance with previous work [1], at comparable respiration rates and excellent functional quality of mitochondria we detected in brain mitochondria a high reversed electron flow-dependent H2O2 generation while the bc1-complex-dependent H2O2 generation in the presence of succinate+antimycin was low. On the other hand, the reversed electron flow-dependent superoxide generation rate was small while the bc1-complex-dependent superoxide production was considerable. In contrast, isolated skeletal muscle mitochondria showed at almost comparable reversed electron flow-dependent H2O2 generation more than ten-fold higher bc1-complex-dependent superoxide and H2O2 generation. Our data are compatible with the following suppositions: (i) The major ROS generation site in complex I visible during reversed electron flow (very likely the FMN semiquinone moiety) is liberating superoxide predominantly to the mitochondrial matrix space. (ii) Similarly, the bc1-complex-dependent superoxide generation site (the semiquinone at center o) liberates superoxide to both compartments with certain preference to the cytosolic space (in accordance with [2]). (iii) Muscle mitochondria, most likely due to their higher endogenous CoQ content, generate at comparable maximal rates of respiration considerable larger amounts of superoxide at center o of complex III [3]. These findings imply a considerable role of mitochondrial complex I dependent ROS generation for pathologies of the brain, like epilepsy and neurodegenerative diseases.

1.  Kudin AP, Bimpong-Buta NY, Vielhaber S, Elger CE, Kunz WS (2004) Characterization of superoxide-producing sites in isolated brain mitochondria. J. Biol. Chem. 279: 4127-4135.

2.  St-Pierre J, Buckingham JA, Roebuck SJ, Brand MD (2002) Topology of superoxide production from different sites in the mitochondrial transport chain. J. Biol. Chem. 277: 44784-44790.

3.  Kudin AP, Debska-Vielhaber G, Kunz WS (2005) Characterization of superoxide-producing sites in isolated rat brain and skeletal muscle mitochondria. Biomed. Pharmacother. 59: 163-168.


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