The Acanthamoeba castellanii mitochondria contain an uncoupling protein (AcUCP) which dissipates the proton electrochemical gradient built up by respiratory chain. In isolated, phosphorylating A. castellanii mitochondria the proton re-uptake mediated by free fatty acid-activated AcUCP is inhibited by purine nucleotide (GTP) only when quinone (Q) is sufficiently oxidized. In isolated A. castellanii mitochondria respiring in state 4 with external NADH or succinate, the linoleic acid-induced uncoupling protein activity is not affected by purine nucleotide (GDP) when Q reducing pathway is uninhibited. The progressive decrease of state 4 respiration by limitation of respiratory substrates availability leads to a full inhibitory effect of GDP. As the inhibitory effect of GDP is observed only when Q-reducing pathway is decreased, we conclude that the inhibition of free fatty acid activated AcUCP by purine nucleotides depends on coenzyme Q redox state, not only in phosphorylating mitochondria, but also in non-phosphorylating respiration. This indicates that Q redox state could be a metabolic sensor for purine nucleotide inhibition of FFA-activated UCP, universal for both: resting and phosphorylating respiration.

This work was supported by grants from the Polish agencies: The Ministry of Scientific Research (0252/P01/2007/32) and AMU Faculty of Biology (PBWB 701/2006).

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1. ATP-sensitive potassium channel in mitochondria of the eukaryotic microorganism, Acanthamoeba castellanii
2. Regulation of the energy-dissipating systems in Acanthamoeba castellanii mitochondria by purine nucleotides