How proapoptotic proteins can escape from mitochondria?

Some proapoptotic proteins (cytochrome c, apoptosis-inducing factor (AIF) and certain procaspases) are normally localized in the intermembrane space of mitochondria and escape to the cytosol when apoptosis is initiated. There are two mechanisms for release of the above proteins from mitochondria, namely (i) an increase in permeability of the outer mitochondrial membrane for proteins, and (ii) an increase in permeability of the inner mitochondrial membrane for small solutes (permeability transition pore, PTP), causing swelling of mitochondrial matrix, which in turn results in disruption of the outer membrane of the organelles. There is not a single piece of evidence for localization of proapoptotic proteins in the matrix and their release via PTP to the cytosol as shown in a cartoon in Voehringer’s paper.