Denaturation of purple membranes at the air/water interface studied by SEM

Fragments of purple membrane were spread at the air/water interface. The interfacial films were transferred onto a silicon wafer with time and initial coverage taken as parameters. The structure of the transferred films was examined with a scanning electron microscope. It was shown that both the size and the packing density of the membrane fragments decreased rapidly with time when the initial coverage was low, and that the intermembrane region was occupied by some substances. An assay by SDS polyacrylamide gel electrophoresis of a built-up film showed that bacteriorhodopsin molecules existed also in the intermembrane region. These results indicated that the denaturation of the purple membrane or the unfolding of bacteriorhodopsin occurred from the periphery of a membrane fragment at the air/water interface.