An X-ray diffraction study on a single rod outer segment from frog retina.

X-ray diffraction patterns were recorded from isolated single rod outer segments of frog. The outer segments in Ringer's solution were exposed to a 6 µm microbeam (15 keV) at the BL40XU beamline, SPring-8. The diffraction pattern demonstrated a remarkable regularity in the stacking and flatness of the disk membranes. The electron density profile calculated from the intensity of up to tenth-order reflections showed a pair of bilayers that comprise a disk membrane. The structure of the disk membrane and the changes in the profile on swelling generally agreed with previous reports. Radiation damage was significant with an irradiation of 5 × 10(5) Gy which is much lower than the known damaging dose on proteins at the liquid-nitrogen temperature.