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

Authors:

• Andrzej Woyda-Płoszczyca,
• Wiesława Jarmuszkiewicz

Abstract

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 mitochondrial 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 HNEinduced AcUCP in phosphorylating respiration vary when the rate of succinate oxidation is decreased by limi ting succinate uptake or inhibiting complex III acti vity within the range of a constant membrane potential. In phosphorylating mitochondria, at a given HNE concentration (100 μm ), the efficiency of AcUCP in mitochondrial uncoupling 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 sensitivity of AcUCP activity to GTP depends on the redox state of the membranous ubiquinone.