Identification and characterization of the pore-forming protein in the outer membrane of rat liver mitochondria.

The proteins of the outer membrane from rat liver mitochondria have been subfractionated by means of density gradient centrifugation. The different polypeptides of the membrane were incorporated into asolectin vesicles and black lipid membranes. It was observed that a polypeptide of Mr 32 000 renders asolectin vesicles permeable to ADP and forms pores in bilayer membrane. These pores showed the same properties as the channels which are formed in the lipid membrane after addition of Triton X-100 solubilized complete outer membrane. The properties of the pore are as follows: (1) The formation of pores depends on the type of phospholipid used for the preparation of the black membranes. (2) The pore is inserted asymmetrically into the membrane. (3) The pore is voltage gated but does not switch off completely at higher voltages. The pore seems to show different conductance states decreasing conductance being observed at increasing voltage. The implications of these findings for the regulation of transport processes across the outer membrane are discussed.