Lipid-water interface mediates reversible ionophore conformational change.

A new procedure of conformational analysis was used to demonstrate that the ionophore conformation is mediated by its membrane environment. In the hydrophobic lipid matrix, the ionomycin-Ca++ complex adopts a conformation well suited for translocation across the interior of the membrane whereas at the lipid-water interface, the Ca++ ion is immersed into the aqueous phase in a position favorable to its complexation or decomplexation. The translocation of Ca++ across the lipid bilayer supposes a reversible transformation of the two conformers. The conformational analysis shows how the dielectric constant discontinuity existing at the lipid-water interface mediates the reversible transformation of one structure into the other.