It catalyzes the reduction of cytochrome c by
oxidation of coenzyme Q (CoQ) and the concomitant pumping of 4 protons from the mitochondrial matrix to the intermembrane space:
: QH + 2 cytochrome c (Fe)  + 2 H → Q + 2 cytochrome c (Fe) + 4 H
In the process called Q cycle, two protons are consumed from the matrix (M), four protons are released into the inter membrane space (IM) and two electrons are passed to cytochrome c.