Hydroxynonenal-stimulated activity of the uncoupling protein in Acanthamoeba castellanii mitochondria under phosphorylating conditions.

The influence of 4-hydroxy-2-nonenal (HNE), a lipid peroxidation end product, on the activity of the amoeba Acanthamoeba castellanii uncoupling protein (AcUCP) in isolated phosphorylating mitochondria was studied. Under phosphorylating conditions, exogenously added HNE induced GTP-sensitive AcUCP-mediated mito-chondrial uncoupling. The HNE-induced proton leak decreased the yield of oxidative phosphorylation in an HNE concentration-dependent manner. The present study describes how the contributions of ATP synthase and HNE-induced AcUCP in phosphorylating respiration vary when the rate of succinate oxidation is decreased by limiting succinate uptake or inhibiting complex III activity within the range of a constant membrane potential. In phos-phorylating mitochondria, at a given HNE concentration (100 fiM), the efficiency of AcUCP in mitochondrial uncou-pling increased as the respiratory rate decreased because the AcUCP contribution remained constant while the ATP synthase contribution decreased with the respiratory rate. HNE-induced uncoupling can be inhibited by GTP only when ubiquinone is sufficiently oxidized, indicating that in phosphorylating A. castellanii mitochondria, the sensi-tivity of AcUCP activity to GTP depends on the redox state of the membranous ubiquinone. [ABSTRACT FROM AUTHOR]

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