[81] X-Ray and neutron diffraction of retinal rod outer segments

Publisher Summary This chapter discusses the X-ray and neutron diffraction of retinal rod outer segments. The regular stacking of the disk membranes in a native retinal rod outer segment (ROS) is particularly useful for physical studies. Because of this stacking and the liquid crystalline nature of the lipids in the membranes, an isolated ROS may be considered a liquid crystal monodomain. The introduction of position-sensitive X-ray detectors considerably reduced the data taking time and allowed physiological studies on perfused retina. Advantage was also taken of the large diamagnetic anisotropy of ROS to record X-ray diffraction data from isolated ROS well oriented in a magnetic field. With the development of improved intensity neutron beams at high flux reactors the diffraction approach has been extended to neutrons. Diffraction patterns are qualitatively similar for X-rays and neutrons of comparable wavelength: the pattern geometry is defined by the ROS morphology and the beam wavelength.