LIPID AND LIPID PROTEIN MONOLAYERS SPREAD FROM A VESICLE SUSPENSION - A MICROFLUORESCENCE FILM BALANCE STUDY

The process of the formation of a monolayer from a vesicle suspension for the two lecithins DMPC and DPPC, for the phosphatidic acid DMPA, and for a synthetic proteolipid was investigated. Exchange kinetics between vesicles and a monolayer as well as equilibrium spreading pressure of the above substances were determined for different temperatures. The resulting monolayers were separated from the vesicle phase and characterized by film balance microfluorescence techniques. Pressure-area diagrams were taken. Simultaneously the lateral distribution of a fluorescent probe that was a minor constituent of the monolayer was recorded. The data of the pure lipid films were compared with those obtained by the equivalent monolayers spread from an organic solution. The vesicle-spread monolayers were transferred onto solid supports, and the texture and the height distribution of the monolayers were determined. In the case of the lipid-protein monolayer a fluorescence binding assay was carried out after the spreading and transfer procedure. It is shown (1) that the vesicle-spread monolayers are separable from the vesicles, (2) that within the framework of our study their properties do not differ from the equivalent monolayers that were spread from an organic solution, (3) that their composition is the same as that of the vesicles, and (4) that the technique employed here enables one to transfer certain membrane-bound proteins from the vesicle phase via the air-water interface onto solid supports retaining their functionality. Furthermore, a model for the lipid exchange between the vesicles and the monolayer is suggested. © 1990 American Chemical Society.