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1

Response of Acanthamoeba castellanii mitochondria to oxidative stress

100%

Trocha L. K., Stobienia O.

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2007

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vol. 54

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issue 4

797-803

EN

The purpose of this study was to examine the effects of oxidative stress caused by hydroperoxide (H2O2) in the presence of iron ions (Fe2+) on mitochondria of the amoeba Acanthamoeba castellanii. We used isolated mitochondria of A. castellanii and exposed them to four levels of H2O2 concentration: 0.5, 5, 15, and 25 mM. We measured basic energetics of mitochondria: oxygen consumption in phosphorylation state (state 3) and resting state (state 4), respiratory coefficient rates (RC), ADP/O ratios, membrane potential (ΔΨm), ability to accumulate Ca2+ , and cytochrome c release. Our results show that the increasing concentrations of H2O2 stimulates respiration in states 3 and 4. The highest concentration of H2O2 caused a 3-fold increase in respiration in state 3 compared to the control. Respiratory coefficients and ADP/O ratios decreased with increasing stress conditions. Membrane potential significantly collapsed with increasing hydroperoxide concentration. The ability to accumulate Ca2+ also decreased with the increasing stress treatment. The lowest stress treatment (0.5 mM H2O2) significantly decreased oxygen consumption in state 3 and 4, RC, and membrane potential. The ADP/O ratio decreased significantly under 5 mM H2O2 treatment, while Ca2+ accumulation rate decreased significantly at 15 mM H2O2. We also observed cytochrome c release under increasing stress conditions. However, this release was not linear. These results indicate that as low as 0.5 mM H2O2 with Fe2+ damage the basic energetics of mitochondria of the unicellular eukaryotic organism Acanthamoeba castellanii.

2

The access of metabolites into yeast mitochondria in the presence and absence of the voltage dependent anion selective channel (YVDAC1)

81%

Kmita H., Stobienia O., Michejda J.

Acta Biochimica Polonica

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1999

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vol. 46

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issue 4

991-1000

EN

Since yeast Saccharomyces cerevisiae mutants depleted of the voltage dependent anion selective channel (YVDAC1) are still able to grow on a non-fermentable carbon source, a functional transport system in the outer mitochondrial membrane must exist to support the access of metabolites into mitochondria. It was assumed that the properties of the system could be inferred from the differences in the results observed between wild type and mutant mitochondria since no crucial differences in this respect between the two types of mitoplasts were observed. YVDAC1-depleted mitochondria displayed a highly reduced permeability of the outer membrane, which was reflected in increased values of K^{NADH}_{0.5} for respiration and K^{ADP}_{0.5} for triggering phosphorylating state as well as in delayed action of carboxyatractylate (CATR) in inhibition of phosphorylating state. The parameters were chosen to express the accessibility of the applied species to the intermembrane space. The passage of the molecules through the outer membrane depleted of YVDAC1 could be partially improved in the presence of bivalent cations (Mg^{2+}, Ca^{2+}), as in their presence lower values of the calculated parameters were obtained. The restrictions imposed on the transport of molecules through the YVDAC1-depleted outer membrane resulted in a competition between them for the access to the intermembrane space as measured by changes in parameters observed for a given species in the presence of another one. The competition was stronger in the absence of Mg^{2+} and depended on charge and size of transported molecules, as the strongest competitor was CATR and the weakest one - {NADH}. Thus, it can be concluded that the transport system functioning in the absence of YVDAC1 is modulated by bivalent cations and charge as well as size of transported molecules. Since an increased level of respiration due to the dissipation of Δψ causes an increase of K^{NADH}_{0.5} in both wild type and YVDAC1-depleted mitochondria it is concluded that a common property of YVDAC1 and the system functioning in YVDAC1-depleted mitochondria seems to be the dependence of the capacity on the level of mitochondrial respiration.

3

Modulation of the voltage-dependent anion-selective channel by cytoplasmic proteins from wild type and the channel depleted cells of Saccharomyces cerevisiae.

81%

Kmita H., Budzińska M., Stobienia O.

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2003

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vol. 50

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issue 2

415-424

EN

It is well known that effective exchange of metabolites between mitochondria and the cytoplasm is essential for cell physiology. The key step of the exchange is transport across the mitochondrial outer membrane, which is supported by the voltage-dependent anion-selective channel (VDAC). Therefore, it is clear that the permeability of VDAC must be regulated to adjust its activity to the actual cell needs. VDAC-modulating activities, often referred to as the VDAC modulator, were identified in the intermembrane space of different organism mitochondria but the responsible protein(s) has not been identified as yet. Because the VDAC modulator was reported to act on VDAC of intact mitochondria when added to the cytoplasmic side it has been speculated that a similar modulating activity might be present in the cytoplasm. To check the speculation we used mitochondria of the yeast Saccharomyces cerevisiae as they constitute a perfect model to study VDAC modulation. The mitochondria contain only a single isoform of VDAC and it is possible to obtain viable mutants devoid of the channel (Δpor1). Moreover, we have recently characterised a VDAC-modulating activity located in the intermembrane space of wild type and Δpor1 S. cerevisiae mitochondria. Here, we report that the cytoplasm of wild type and Δpor1 cells of S. cerevisiae contains a VDAC-modulating activity as measured in a reconstituted system and with intact mitochondria. Since quantitative differences were observed between the modulating fractions isolated from wild type and Δpor1 cells when they were studied with intact wild type mitochondria as well as by protein electrophoresis it might be concluded that VDAC may influence the properties of the involved cytoplasmic proteins. Moreover, the VDAC-modulating activity in the cytoplasm differs distinctly from that reported for the mitochondrial intermembrane space. Nevertheless, both these activities may contribute efficiently to VDAC regulation. Thus, the identification of the proteins is very important.

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1 Trocha L. K.

Response of Acanthamoeba castellanii mitochondria to oxidative stress

The access of metabolites into yeast mitochondria in the presence and absence of the voltage dependent anion selective channel (YVDAC1)

Modulation of the voltage-dependent anion-selective channel by cytoplasmic proteins from wild type and the channel depleted cells of Saccharomyces cerevisiae.