Effect of cardiolipin on proton permeability of phospholipid liposomes: The role of hydration at the lipid-water interface

The effect of cardiolipin on the proton permeability of dipalmitoyl-phospha tidylcholine small unilamellar vesicles was examined by utilizing the pH-de pendent fluorescence emission of 5- (and 6-) carboxyfluorescein, It has bee n found that the proton permeability of the phospholipid bilayer was greatl y enhanced in the presence of cardiolipin, an acidic phospholipid mainly fo und in the inner mitochondrial membranes. In the presence of bovine heart c ardiolipin, the bilayer surface hydration, as assessed with the fluorescenc e lifetime of 1-anilinonaphthalene-8-sulfonic acid, was increased, while hy dration in the acyl chain region was not altered. In addition, the bilayer fluidity was also not affected. Taken together, these results suggest that the Lipid-water interface is the major energy barrier for proton permeation of the bilayer vesicles, and alteration to properties of this interface by cardiolipin headgroup appears to be responsible for the enhanced proton pe rmeability, (C) 2001 Academic Press.