The key role of the energized state of Saccharomyces cerevisiae mitochondria in modulations of the outer membrane channels by the intermembrane space proteins.

Mitochondria of the yeast Saccharomyces cerevisiae constitute a perfect model to study the outer membrane channel modulation as besides the TOM complex channel they contain only a single isoform of the VDAC channel and it is possible to obtain viable mutants devoid of the channel. Here, we report that the fraction of the intermembrane space isolated from wild type and the VDAC channel-depleted yeast mitochondria, except of the well-known VDAC channel modulator activity, displays also the TOM complex channel modulating activity as measured in the reconstituted system and with intact mitochondria. The important factor influencing the action of both modulating activities is the energized state of mitochondria. Moreover, the presence of the VDAC channel itself seems to be crucial to properties of the intermembrane space protein(s) able to modulate the outer membrane channels because in the case of intact mitochondria quantitative differences are observed between modulating capabilities of the fractions isolated from wild type and mutant mitochondria.