Computational modeling analysis of mitochondrial superoxide production under varying substrate conditions and upon inhibition of different segments of the electron transport chain

A computational mechanistic model of superoxide (O-2(center dot-) formation in the mitochondrial electron transport chain (ETC) was developed to facilitate the quantitative analysis of factors controlling mitochondrial O-2(center dot-) production and assist in the interpretation of experimental studies. The model takes into account all individual electron transfer reactions in Complexes I and III. The model accounts for multiple, often seemingly contradictory observations on the effects of Delta Psi and Delta pH, and for the effects of multiple substrate and inhibitor conditions, including differential effects of Complex III inhibitors antimycin A, myxothiazol and stigmatellin. Simulation results confirm that, in addition to O-2(center dot-) formation in Complex III and at the flavin site of Complex I, the quinone binding site of Complex I is an additional superoxide generating site that accounts for experimental observations on O-2(center dot-) production during reverse electron transfer. However, our simulation results predict that, when cytochrome c oxidase is inhibited during oxidation of succinate, ROS production at this site is eliminated and almost all superoxide in Complex I is generated by reduced FMN, even when the redox pressure for reverse electron transfer from succinate is strong. In addition, the model indicates that conflicting literature data on the kinetics of electron transfer in Complex III involving the iron-sulfur protein-cytochrome bL complex can be resolved in favor of a dissociation of the protein only after electron transfer to cytochrome bH. The model predictions can be helpful in understanding factors driving mitochondrial superoxide formation in intact cells and tissues. (C) 2015 Elsevier B.V. All rights reserved.