Molecular organization in protein-lipid film on the water surface studied by x-ray standing wave measurements under total external reflection

The x-ray standing wave method has been applied to study self-assembling processes in a protein-lipid film formed by injecting the protein-lipid mixture of alkaline phosphatase and phosphatidylinositol under the phospholipid monolayer preliminarily deposited on the water subphase by Langmuir method. X-ray standing wave measurements allowed to determine the composition of the protein-lipid film and to locate ions position in the direction normal to the film surface. The presence of trace Ni contamination incorporated in the protein-lipid film from the water subphase has been established. Numerical analysis of the X-ray standing wave fluorescence data revealed that after injection under the phospholipid monolayer, the protein-lipid mixture separated in a self-assembled manner to layered structure, molecules of alkaline phosphatase arranged themselves into a pure protein layer containing no phospholipid molecules.