Molecular recognition of complementary liposomes: The enhancing role of cholesterol

Liposomes based on hydrogenated phosphatidylcholine (PC) incorporating dihe xadecyl phosphate (DHP) and 1-(4-(dihexadecylcarbamoyl) butyl)guanidinium p -toluene sulfonate (DBG), respectively, were mixed in aqueous dispersion at room temperature, and their molecular recognition effectiveness was invest igated by turbidimetric measurements, microscopy, DSC, and isothermal titra tion calorimetry. Because of the high binding efficiency of the incorporate d recognizable lipids, accurate results could be obtained for low DHP/PC an d DBG/PC molar ratios (19:1), especially for enthalpy change measurements. The liposome-liposome interaction was further investigated as a function of the cholesterol content in mixed (PC-cholesterol) liposomes. At appropriat e cholesterol concentrations, the organization of the recognizable moieties within the liquid-ordered phase of the bilayer membrane enhances molecular recognition at the liposomal interface.