Mitochondria of Acanthamoeba castellanii (Protozoa), posses energy-dissipating systems: (i) a cyanide-resistant alternative oxidase (AOX), (ii) a free fatty acid-activated uncoupling protein (UCP), and recently discovered (iii) an ATP-sensitive potassium channel (mitoKATP). The activity of these systems, thereby the efficiency of oxidative phosphorylation, is regulated by guanosine and adenosine 5'-phosphates in a different way. The activity of the AOX is stimulated significantly by guanine nucleotides (GMP, GDP, GTP) and slightly by adenine nucleotides (AMP, ADP). By contrast the activity of the UCP is inhibited by the tri- and diphosphate nucleosides, while the inhibition by monophosphate nucleosides is negligible. On the other hand, in the case of the mitoKATP, its sensitivity to purine nucleotides is not yet well described besides the inhibition by ATP. It is noteworthy that in A. castellanii mitochondria, ATP inhibits all these three systems including the alternative oxidase (reported here for the first time). Therefore it indicates that ATP is a key modulator in the maintaining of the energetic and metabolic balance during the life of this unicellular organism.

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1. ATP-sensitive potassium channel in mitochondria of the eukaryotic microorganism, Acanthamoeba castellanii
2. Acanthamoeba castellanii mitochondrial uncoupling protein activity is regulated by redox state of ubiquinone.