SQUEEZING OF OIL-SWOLLEN SURFACTANT BILAYERS BY A MEMBRANE-PROTEIN

We have performed small angle x-ray scattering experiments on a ternar y system made of a nonionic surfactant, dodecane, and water, in the ab sence and upon insertion of a transmembrane protein. In contrast to ot her proteins or polymers studied, its incorporation reduces the Bragg spacing from 200 Angstrom to 80 Angstrom, which scales as c(-0.5), whe re c is the protein surface density. The macromolecule incorporated in to the hydrophobic part of the lamellar phase appears on freeze-fractu re electron micrographs as intramembranous particles. The data are fit ted by a simple model of thermally undulating lamellae decorated with protein molecules.