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See detailThe effect of pH on the alternative oxidase activity in isolated Acanthamoeba castellanii mitochondria.
Jarmuszkiewicz, W.; Hryniewiecka, L.; Sluse, Francis ULg

in Journal of Bioenergetics & Biomembranes (2002), 34(3), 221-226

Mitochondria of Acanthamoeba castellanii possess a cyanide-resistant GMP-stimulated ubiquinol alternative oxidase in addition to the cytochrome pathway. In a previous work it has been observed that an ... [more ▼]

Mitochondria of Acanthamoeba castellanii possess a cyanide-resistant GMP-stimulated ubiquinol alternative oxidase in addition to the cytochrome pathway. In a previous work it has been observed that an interaction between the two ubiquinol-oxidizing pathways exists in intact A. castellanii mitochondria and that this interaction may be due to a high sensitivity of the alternative oxidase to matrix pH. In this study we have shown that the alternative oxidase activity reveals a pH-dependence with a pH optimum at 6.8 whatever the reducing substrate may be. The GMP stimulation of alternative oxidase is also strongly dependent on pH implicating probably protonation/deprotonation processes at the level of ligand and protein with an optimum pH at 6.8. The ubiquinone redox state-dependence of alternative oxidase activity is modified by pH in such a way that the highest activity for a given ubiquinone redox state is observed at pH 6.8. Thus pH, binding of GMP, and redox state of ubiquinone collaborate to set the activity of the GMP-stimulated alternative oxidase in isolated A. castellanii mitochondria. The high pH sensitivity of the alternative oxidase could link inactivation of the cytochrome pathway proton pumps to activation of the alternative oxidase with acceleration of redox free energy dissipation as a consequence. [less ▲]

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See detailInteractions between the cytochrome pathway and the alternative oxidase in isolated Acanthamoeba castellanii mitochondria.
Jarmuszkiewicz, W.; Sluse, Francis ULg; Hryniewiecka, L. et al

in Journal of Bioenergetics & Biomembranes (2002), 34(1), 31-40

The steady-state activity of the two quinol-oxidizing pathways of Acanthamoeba castellanii mitochondria, the phosphorylating cytochrome pathway (i.e. the benzohydroxamate(BHAM)-resistant respiration in ... [more ▼]

The steady-state activity of the two quinol-oxidizing pathways of Acanthamoeba castellanii mitochondria, the phosphorylating cytochrome pathway (i.e. the benzohydroxamate(BHAM)-resistant respiration in state 3) and the alternative oxidase (i.e. the KCN-resistant respiration), is shown to be fixed by ubiquinone (Q) pool redox state independently of the reducing substrate (succinate or exogenous reduced nicotinamide adenine dinucleotide (NADH)), indicating that the active Q pool is homogenous. For both pathways, activity increases with the Q reduction level (up to 80%). However, the cytochrome pathway respiration partially inhibited (about 50%) by myxothiazol decreases when the Q reduction level increases above 80%. The decrease can be explained by the Q cycle mechanism of complex III. It is also shown that BHAM has an influence on the relationship between the rate of ADP phosphorylation and the Q reduction level when alternative oxidase is active, and that KCN has an influence on the relationship between the alternative oxidase activity and the Q reduction level. These unexpected effects of BHAM and KCN observed at a given Q reduction level are likely due to functional connections between the two pathways activities or to protein-protein interaction. [less ▲]

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See detailEfficiency of Acanthamoeba castellanii uncoupling protein in energy-dissipating processes
Jarmuszkiewicz, W.; Hryniewiecka, L.; Sluse-Goffart, C. et al

in Hofmeyr, J.; Rohwer, J. M.; Snoops, J. L. (Eds.) Biothermokinetic 2000 : Animating the cellular map (2000)

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See detailIdentification and characterization of a protozoan uncoupling protein in Acanthamoeba castellanii.
Jarmuszkiewicz, W.; Sluse-goffart, C.; Hryniewiecka, L. et al

in Journal of Biological Chemistry (1999), 274(33), 23198-23202

An uncoupling protein (UCP) has been identified in mitochondria from Acanthamoeba castellanii, a nonphotosynthetic soil amoeboid protozoon that, in molecular phylogenesis, appears on a branch basal to the ... [more ▼]

An uncoupling protein (UCP) has been identified in mitochondria from Acanthamoeba castellanii, a nonphotosynthetic soil amoeboid protozoon that, in molecular phylogenesis, appears on a branch basal to the divergence points of plants, animals, and fungi. The existence of UCP in A. castellanii (AcUCP) has been revealed using antibodies raised against plant UCP. Its molecular mass (32,000 Da) was similar to those of plant and mammalian UCPs. The activity of AcUCP has been investigated in mitochondria depleted of free fatty acids. Additions of linoleic acid stimulated state 4 respiration and decreased transmembrane electrical potential (DeltaPsi) in a manner expected from fatty acid cycling-linked H(+) reuptake. The half-maximal stimulation by linoleic acid was reached at 8.1 +/- 0.4 microM. Bovine serum albumin (fatty acid-free), which adsorbs linoleic acid, reversed the respiratory stimulation and correspondingly restored DeltaPsi. AcUCP was only weakly inhibited by purine nucleotides like UCP in plants. A single force-flow relationship has been observed for state 4 respiration with increasing concentration of linoleic acid or of an uncoupler and for state 3 respiration with increasing concentration of oligomycin, indicating that linoleic acid has a pure protonophoric effect. The activity of AcUCP in state 3 has been evidenced by ADP/oxygen atom determination. The discovery of AcUCP indicates that UCPs emerged, as specialized proteins for H(+) cycling, early during phylogenesis before the major radiation of phenotypic diversity in eukaryotes and could occur in the whole eukaryotic world. [less ▲]

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See detailDetermination of the respective contributions of energy-dissipating athways to mitochondrial respiration : The ADP/O method
Sluse, Francis ULg; Jarmuszkiewicz, W.; Almeida, A. et al

in Moller, I. M.; Gardestrom, P.; Glimelius, K. (Eds.) et al Plant mitochondria : from gene to function (1998)

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See detailElectron partitioning between the two branching quinol-oxidizing pathways in Acanthamoeba castellanii mitochondria during steady-state state 3 respiration.
Jarmuszkiewicz, W.; Sluse-Goffart, C.; Hryniewiecka, L. et al

in Journal of Biological Chemistry (1997), 273(17), 10174-10180

Amoeba mitochondria possess a respiratory chain with two quinol-oxidizing pathways: the cytochrome pathway and the cyanide-resistant alternative oxidase pathway. The ADP/O method, based on the non ... [more ▼]

Amoeba mitochondria possess a respiratory chain with two quinol-oxidizing pathways: the cytochrome pathway and the cyanide-resistant alternative oxidase pathway. The ADP/O method, based on the non-phosphorylating property of alternative oxidase, was used to determine contributions of both pathways in overall state 3 respiration in the presence of GMP (an activator of the alternative oxidase in amoeba) and succinate as oxidizable substrate. This method involves pair measurements of ADP/O ratios plus and minus benzohydroxamate (an inhibitor of the alternative oxidase). The requirements of the method are listed and verified. When overall state 3 respiration was decreased by increasing concentrations of n-butyl malonate (a non-penetrating inhibitor of succinate uptake), the quinone reduction level declined. At the same time, the alternative pathway contribution decreased sharply and became negligible when quinone redox state was lower than 50%, whereas the cytochrome pathway contribution first increased and then passed through a maximum at a quinone redox state of 58% and sharply decreased at a lower level of quinone reduction. This study is the first attempt to examine the steady-state kinetics of the two quinol-oxidizing pathways when both are active and to describe electron partitioning between them when the steady-state rate of the quinone-reducing pathway is varied. [less ▲]

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See detailDetermination of the respective contributions of the cytochrome and alternative oxidase pathway in Acanthamoeba catellanii
Jarmuszkiewicz, W.; Sluse-Goffart, C.; Hryniewiecka, L. et al

in Westerhoff, H.; Snoep, J.; Sluse, Francis (Eds.) et al Biothermokinetics of the living cell (1996)

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