Fig. 3. Ratio between interface [H⁺] and bulk [H⁺] ([H⁺]_inf/[H⁺]_bulk) plotted against the molar ratio of charged lipids (X_TOCL/DOPG and X_DOPG). (A) Plots of [H⁺]_inf/[H⁺]_bulk against TOCL ratio ([TOCL]/([DOPC] + [DOPE] + [TOCL])) for DOPC/DOPE/TOCL LUVs (total lipid, 2.0 mM) at various bulk pHs: dark yellow, pH 6.0; blue, pH 6.5; red, pH 7.0. The DOPC : DOPE ratio was kept constant at 2 : 1. The plots of [H⁺]_inf/[H⁺]_bulk against DOPG ratio for DOPG/DOPC LUVs at pH 5.0 are also shown (black). (B) Extended plots of [H⁺]_inf/[H⁺]_bulk against DOPG ratio for DOPG/DOPC LUVs. The absorption intensities of RHG were saturated under the TOCL and DOPG concentrations used. Measurements were performed at 25 °C.