Liposomal membranes. XI. A suggestion to structural characteristics of acido-thermophilic bacterial membranes.

To understand the role of omega-cyclohexyl fatty acid residue of lipids in acido-thermophilic bacterial membranes, three unusual phosphatidylcholines, 1, 2-di-11-cyclohexylundecanoyl-L-alpha-phosphatidylcholine (11CYPC), 1,2-di-13-cyclohexyltridecanoyl-L-alpha-phosphatidylcholine (13CYPc), and 1-13-cyclohexyltridecanoyl-2-11-cyclohexylundecanoyl-L-alpha- phosphatidylcholine (1-13CY-2-11CYPC) were prepared and the steady-state fluorescence anisotropy of 1, 6-diphenylhexatriene (DPH) in the hydrophobic domain of these liposomal bilayers was determined. Compared with the case of dipalmitoyl (DPPC) or dimyristoyl phosphatidylcholine (DMPC), introducing the omega-cyclohexyl moiety onto lecithins makes the bilayers fluid below the phase transition temperature, while immobilizes them above the phase transition temperatures. The properties of the unusual phosphatidylcholine liposomes suggested by the steady-state fluorescence anisotropy investigation were in good agreement with those obtained from the thermotropic and permeability investigations. Results obtained are discussed from the view point of the role and function of lipid membranes of acido-thermophilic bacteria which contain unusual fatty acids.