In phosphorylating Acanthamoeba castellanii mitochondria the sensitivity of uncoupling protein activity to GTP depends on the redox state of quinone.
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in Journal of Bioenergetics & Biomembranes (2005), 37
In isolated Acanthamoeba castellanii mitochondria respiring in state 3 with external NADH or succinate, the linoleic acid-induced purine nucleotide-sensitive uncoupling protein activity is able to ... [more ▼]
In isolated Acanthamoeba castellanii mitochondria respiring in state 3 with external NADH or succinate, the linoleic acid-induced purine nucleotide-sensitive uncoupling protein activity is able to uncouple oxidative phosphorylation. The linoleic acid-induced uncoupling can be inhibited by a purine nucleotide (GTP) when quinone (Q) is sufficiently oxidized, indicating that in A. castellanii mitochondria respiring in state 3, the sensitivity of uncoupling protein activity to GTP depends on the redox state of the membranous Q. Namely, the inhibition of the linoleic acid-induced uncoupling by GTP is not observed in uninhibited state 3 respiration as well as in state 3 respiration progressively inhibited by complex III inhibitors, i.e., when the rate of quinol (QH(2))-oxidizing pathway is decreased. On the contrary, the progressive decrease of state 3 respiration by declining respiratory substrate availability (by succinate uptake limitation or by decreasing external NADH concentration), i.e., when the rate of Q-reducing pathways is decreased, progressively leads to a full inhibitory effect of GTP. Moreover, in A. castellanii mitochondria isolated from cold-treated cells, where a higher uncoupling protein activity is observed, the inhibition of the linoleic acid-induced proton leak by GTP is revealed for the same low values of the Q reduction level. [less ▲]Detailed reference viewed: 12 (1 ULg)
The effect of growth at low temperature on the activity and expression of the uncoupling protein in Acanthamoeba castellanii mitochondria.
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in FEBS Letters (2004), 569
Mitochondria of amoeba Acanthamoeba castellanii, a non-photosynthetic soil amoeboid protozoon, possess an uncoupling protein (AcUCP) that mediates free fatty acid-activated proton re-uptake dissipating ... [more ▼]
Mitochondria of amoeba Acanthamoeba castellanii, a non-photosynthetic soil amoeboid protozoon, possess an uncoupling protein (AcUCP) that mediates free fatty acid-activated proton re-uptake dissipating the proton electrochemical gradient built up by respiration. The present study provides the first evidence that UCP could be a cold response protein in unicellulars. In mitochondria isolated from an amoeba batch culture grown temporarily at low temperature (6 degrees C), the content of AcUCP was increased and correlated with an increase in the linoleic acid (LA)-stimulated UCP-mediated carboxyatractyloside-resistant state 4 respiration, as compared to a control culture (routinely grown at 28 degrees C). Moreover, the cytochrome pathway activity was found to be insensitive to the cold exposure of amoeba cells, as indicated by respiration and membrane potential measurements as well as by an absence of change in the adenine nucleotide translocator and cytochrome oxidase expression levels. Furthermore, in mitochondria from the low-temperature-grown cells, at fixed LA concentration, the increased contribution of AcUCP activity to total mitochondrial phosphorylating respiration accompanied by lower coupling parameters was found, as was confirmed by calculation of this contribution using ADP/O measurements. [less ▲]Detailed reference viewed: 8 (1 ULg)