Modular kinetic analysis reveals differences in Cd2+ and Cu2+ ion-induced impairment of oxidative phosphorylation in liver

Abstract

Impaired mitochondrial function contributes to copper- and cadmium-induced cellular dysfunction. In this study, we used modular kinetic analysis and metabolic control analysis to assess how Cd2+ and Cu2+ ions affect the kinetics and control of oxidative phosphorylation in isolated rat liver mitochondria. For the analysis, the system was modularized in two ways: (a) respiratory chain, phosphorylation and proton leak; and (b) coenzyme Q reduction and oxidation, with the membrane potential (Δψ) and fraction of reduced coenzyme Q as the connecting intermediate, respectively. Modular kinetic analysis results indicate that both Cd2+ and Cu2+ ions inhibited the respiratory chain downstream of coenzyme Q. Moreover, Cu2+, but not Cd2+ ions stimulated proton leak kinetics at high Δψ values. Further analysis showed that this difference can be explained by Cu2+ ion-induced production of reactive oxygen species and membrane lipid peroxidation. In agreement with modular kinetic analysis data, metabolic control analysis showed that Cd2+ and Cu2+ ions increased control of the respiratory and phosphorylation flux by the respiratory chain module (mainly because of an increase in the control exerted by cytochrome bc1 and cytochrome c oxidase), decreased control by the phosphorylation module and increased negative control of the phosphorylation flux by the proton leak module. In summary, we showed that there is a subtle difference in the mode of action of Cd2+ and Cu2+ ions on the mitochondrial function, which is related to the ability of Cu2+ ions to induce reactive oxygen species production and lipid peroxidation.