It has been shown recently that the voltage dependent anion selective channel (VDAC) controls the release of the superoxide anion from mitochondria to cytosol. Physiologically, VDAC functions as the major channel allowing passage of metabolites between the intermembrane space of mitochondria and cytoplasm. The channel may be present as isoforms encoded by separated genes, displaying different channel-forming activities and probably playing different roles. In the yeast Saccharomyces cerevisiae two VDAC isoforms have been identified, of which only one was proved to form a channel (VDAC1). The second one (VDAC2) is devoid of a channel-forming activity and its role in the outer mitochondrial membrane is still unclear.

We have shown recently that in the case of S. cerevisiae both VDAC isoforms influence the activity of CuZnSOD located in the mitochondrial intermembrane space and subsequently the expression levels of some mitochondrial proteins in a growth phase dependent way (Budzinska et al, 2007). Here we report that the activity of MnSOD in mitochondria of S. cerevisiae isolated from exponential and stationary phase cells is also distinctly influenced by deletion of a given VDAC isoform. Interestingly, the observed changes are more pronounced in the absence of VDAC2. The differences in MnSOD activities coincide with differences in the mitochondria reduction/oxidation (redox) state as determined by the GSH/total glutathione ratio. Moreover, the absence of a given VDAC isoform results also in an isoform-dependent changes in expression levels of chosen subunits of the mitochondrial outer membrane protein import complexes. Thus, both S. cerevisiae VDAC isoforms seem to be in a functional relationship to the MnSOD activity and the absence of either of them triggers an isoform-related adaptive mechanism probably mediated by changes in mitochondrial redox state. Furthermore, the mitochondrial redox state seems to be functionally coupled to VDAC and this in turn does not require a channel activity.

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1. Fractionation of the membrane β-barrel proteins of the amoeba Acanthamoeba castellanii mitochondria.