Structure of Retinal Photoreceptor Membranes

IN an X-ray diffraction study 1 of the disk membranes of the frog, we derived the profile of average electron density along a line perpendicular to the membrane plane. It was assumed that the membrane consisted basically of a phospholipid bilayer, and a set of phases in agreement with the bilayer structure was adopted for the X-ray reflexions. Our results were consistent with, and they helped to define, the bilayer, but they did not exclude the possibility that the structure of the membrane might be other than a bilayer. We have now checked the correctness of our assumption and in effect have made a direct determination of the structure by means of X-ray diffraction alone.