Pro- and anti-oxidant activities of the mitochondrial respiratory chain: factors influencing NAD(P)H-induced lipid peroxidation.

This paper is a study of factors influencing the rate of lipid peroxidation in beef heart submitochondrial particles induced by NAD(P)H via the NADH-ubiquinone oxidoreductase (Complex I) of the respiratory chain. In accordance with earlier observations, both NADH and NADPH initiated lipid peroxidation in the presence of ADP-Fe3+. The rate of the reaction, measured as oxygen consumption and formation of thiobarbituric acid reactive substances, was biphasic as a function of NADH concentration, reaching a maximum at low NADH concentrations and then declining. In contrast, the NADPH-initiated lipid peroxidation showed a monophasic concentration profile of hyperbolic character. Rotenone did not eliminate the biphasicity of the NADH-induced reaction, indicating that this was not due to an antioxidant effect of reduced ubiquinone at high NADH concentrations. This conclusion was further supported by the demonstration that extraction of ubiquinone from the particles did not relieve the inhibition of lipid peroxidation by high NADH concentrations. However rhein, another inhibitor of Complex I, eliminated the biphasicity, and even caused a substantial stimulation of the NADH-induced lipid peroxidation in the particles upon extraction of ubiquinone by pentane. No similar effect occurred in the case of NADPH-induced lipid peroxidation. Furthermore, rhein facilitated both NADH- and NADPH-induced lipid peroxidation even in the absence of added ADP-Fe3+, in a fashion similar to that earlier reported with succinate in the presence of theonyltrifluoroacetone. Based on these findings and measurements of the redox states of ubiquinone and cytochromes in the presence of KCN and NADH or NADPH, it is concluded that Complex I may distinguish between electron input from NADH and NADPH by differences in the site(s) of substrate binding and in the pathways and rates of NADH and NADPH oxidation.