Three-dimensional electron microscopical investigation of rhodopsin molecules in the disc membrane of Frog rod outer segments

Abstract

Frog rod outer segment (ROS) disc membranes are investigated by three-dimensional electron microscopy of aperiodic structures. Out of the various chemical constituents of these membranes only the visual pigment rhodopsin is examined. It is suggested that rhodopsin molecules are dumb-bell shaped and it is shown that in small areas they are not statistically arranged. Most rhodopsin molecules are tilted 26±2° away from the position normal to the membrane thus showing angles α<90° or α>90°. Within the small part of the disc membrane investigated the long rhodopsin axes lie in planes parallel to the xy-plane, the y-axis being parallel with the connecting cilium of ROS. In the membrane cut-outs reconstructed there are aggregates of five to nine rhodopsin molecules either with α>90° or α<90° only. In adjacent disc membranes all the bigger aggregates appear at the same site and with the same magnitude of α.