Imaging purple membranes dry and in water with the atomic force microscope

Abstract
Purple membranes were imaged dry and in water with the atomic force microscope. Slowly air-dried purple membranes showed large cracks on one side and narrow cracks on the other side. Purple membranes that were imaged in water adsorbed to mica showed no cracks. The hexagonal arrangement of the bacteriorhodopsin molecules could be seen in the two-dimensional Fourier transform from images obtained in water. Often spots to the fifth order corresponding to about 1.1 nm resolution were observed.