title: Ubiquinol (QH(2)) functions as a negative regulator of purine nucleotide inhibition of Acanthamoeba castellanii mitochondrial uncoupling protein.
abstract: We compared the influence of different adenine and guanine nucleotides on the free fatty acid-induced uncoupling protein (UCP) activity in non-phosphorylating Acanthamoeba castellanii mitochondria when the membranous ubiquinone (Q) redox state was varied. The purine nucleotides exhibit an inhibitory effect in the following descending order: GTP>ATP>GDP>ADP≫GMP>AMP. The efficiency of guanine and adenine nucleotides to inhibit UCP-sustained uncoupling in A. castellanii mitochondria depends on the Q redox state. Inhibition by purine nucleotides can be increased with decreasing Q reduction level (thereby ubiquinol, QH₂ concentration) even with nucleoside monophosphates that are very weak inhibitors at the initial respiration. On the other hand, the inhibition can be alleviated with increasing Q reduction level (thereby QH₂ concentration). The most important finding was that ubiquinol (QH₂) but not oxidised Q functions as a negative regulator of UCP inhibition by purine nucleotides. For a given concentration of QH₂, the linoleic acid-induced GTP-inhibited H(+) leak was the same for two types of A. castellanii mitochondria that differ in the endogenous Q content. When availability of the inhibitor (GTP) or the negative inhibition modulator (QH₂) was changed, a competitive influence on the UCP activity was observed. QH₂ decreases the affinity of UCP for GTP and, vice versa, GTP decreases the affinity of UCP for QH₂. These results describe the kinetic mechanism of regulation of UCP affinity for purine nucleotides by endogenous QH₂ in the mitochondria of a unicellular eukaryote.
authors.affiliation: Laboratory of Bioenergetics, Adam Mickiewicz University, Poznan, Poland.
authors.forename: Andrzej
authors.initials: A
authors.lastname: Woyda-Ploszczyca
authors.forename: Wieslawa
authors.initials: W
authors.lastname: Jarmuszkiewicz
mesh_terms: D048248:Acanthamoeba castellanii / Q000378:metabolism* / Q000502:physiology; D000227:Adenine Nucleotides / Q000494:pharmacology; D016227:Benzoquinones / Q000378:metabolism; D005230:Fatty Acids, Nonesterified / Q000494:pharmacology; D006150:Guanine Nucleotides / Q000494:pharmacology; D006706:Homeostasis; D007473:Ion Channels / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000187:drug effects; D011685:Purine Nucleotides / Q000494:pharmacology*; D012265:Ribonucleotides / Q000494:pharmacology; D014451:Ubiquinone / Q000031:analogs & derivatives* / Q000502:physiology; D000071256:Uncoupling Protein 1
chemical_list: D000227:Adenine Nucleotides; D016227:Benzoquinones; D005230:Fatty Acids, Nonesterified; D006150:Guanine Nucleotides; D007473:Ion Channels; D024101:Mitochondrial Proteins; D011685:Purine Nucleotides; D012265:Ribonucleotides; D000071256:Uncoupling Protein 1; D014451:Ubiquinone; C004532:quinone; C003741:ubiquinol