Variability of conductivity changes in black phosphatidylserine membranes induced by proteins from erythrocyte membranes

The electrical conductivity of black phosphatidylserine membranes, in solutions of 100 mM NaCl, 10 mM sodium phosphate (pH 7.1), is strongly increased by the intrinsic proteins ("strongly bound" protein fraction) from human erythrocyte membranes. The magnitude of the conductivity increase is highly dependent on the maximum pH-value pH* used during the preparation of the protein (8.0 less than or equal to pH* less than or equal 11.8). For each pH*, membrane conductivity lambdaf and protein concentration c are linked by the equation lambdaf=k-cs, k and s being functions only of pH*. The value of s varies between 1.0 (pH* 8) and 4.0 (pH* 10). It is assumed that the protein-induced conducting sites, at least for protein pretreatment at pH less than or equal to 10, are assembled from four protein subunits. The incorporation of the subunits into the lipid bilayer is supposed to occur either as the final tetramer (pH* 8) or as monomers (pH* 10) and possibly dimers (pH* around 9)