THE PROTON PERMEABILITY OF LIPOSOMES MADE FROM MITOCHONDRIAL INNER MEMBRANE PHOSPHOLIPIDS - COMPARISON WITH ISOLATED-MITOCHONDRIA

Unilamellar liposomes with native phospholipid fatty acid composition were prepared from rat liver mitochondrial inner membrane phospholipid s by extrusion in medium containing 50 mM potassium. They were diluted into low potassium medium to establish a transmembrane potassium grad ient. A known membrane potential was imposed by addition of valinomyci n, and proton flux into liposomes was measured. Valinomycin in the ran ge 10 pM-1nM was sufficient to fully establish membrane potential. Val inomycin concentrations above 3 nn? catalyzed additional proton flux a nd were avoided. At 300 pM valinomycin, proton flux depended nonlinear ly on membrane potential. At 160 mV membrane potential the flux was 30 nmol H+/min/mg phospholipid-approximately 5% of the proton leak flux under comparable conditions in isolated mitochondria, indicating that leak pathways through bulk phospholipid bilayer account for only a sma ll proportion of total mitochondrial proton leak.