Purification of Mammalian Porins

Abstract

The matrix space of mitochondria is surrounded by two unit membranes. Whereas the role of the inner membrane in oxidative phosphorylation was studied in full detail in recent years, the role of the mitochondrial outer membrane in the mitochondrial metabolism has been neglected because of its apparently high permeability for small hydrophilic solutes. The mitochondrial outer membrane contains indeed general diffusion pores which explain its high permeability. The component of the membrane responsible for its molecular filter properties is a protein, called porin or VDAC (Benz, 1985). Mitochondrial porins were identified and characterized from a variety of eukaryotic cells by reconstitution experiments with planar lipid bilayers and liposomes (Colombini, 1979, De Pinto et al., 1987). The mitochondrial pore has a diameter of about 2 nm in the open state and is slightly anion selective for low transmembrane potentials. Voltages larger than 20 mV cause the shift of the pore into closed states with reduced permeability towards substrates and a changed selectivity.