Reactive oxygen species generated by the mitochondrial respiratory chain affect the complex III activity via...

The aim of this study was to investigate the effect of reactive oxygen species (ROS), produced by the mitochondrial respiratory chain, on the activity of complex III and on the cardiolipin content in bovine-heart submitochondrial particles (SMP). ROS were produced by treatment of nicotinamide adenine dinucleotide (NADH) respiring SMP with rotenone. This treatment resulted in a production of superoxide anion, detected by the epinephrine method, which was blocked by superoxide dismutase (SOD). Exposure of SMP to mitochondrial-mediated ROS generation resulted in a marked loss of complex III activity and in a parallel loss of mitochondrial cardiolipin content. Both these effects were completely abolished by SOD + catalase. Exogenous added cardiolipin was able to almost completely prevent the ROS-mediated loss of complex III activity. No effect was obtained with other major phospholipid components of the mitochondrial membrane such as phosphatidylcholine and phosphatidylethanolamine, or with peroxidized cardiolipin. The results demonstrate that mitochondrial-mediated ROS generation affects the activity of complex III via peroxidation of cardiolipin, which is required for the functioning of this multisubunit enzyme complex. These results may prove useful in probing molecular mechanisms of ROS-induced peroxidative damage to mitochondria, which have been proposed to contribute to those physiopathological conditions characterized by an increase in the basal production of ROS such as aging, ischemia/reperfusion and chronic degenerative diseases.