FREEZE-FRACTURE ANALYSIS OF PHOTORECEPTOR CELL OUTER SEGMENT DISKS AFTER MINIMAL EXTRACTION OF RHODOPSIN

The outer segment disk membranes in the photoreceptor cells of the guinea pig retinas were analyzed after partial extraction of rhodopsin with cetyltrimethylammonium bromide (CTAB). During the earliest stages of rhodopsin extraction, the particulate structure of the particulate face of the disk membranes becomes less dense with the appearance of smooth areas extending between the particles. These smooth areas could occupy a large part of the particulate membrane face. The disk membranes could still retain a planar structure. A transformation of the disk membranes into small vesicles was also evident and was considered to correspond to a stage where the extraction has progressed beyond the earliest stages. Extraction with digitonin led to an immediate disintegration of the disk membranes into vesicles. Since CTAB can preferentially solubilize rhodopsin without extracting the membrane lipids (Heller, 1968;Biochemistry, 7, 2906), the observations were considered to support the interpretation of Sjöstrand and Kreman (1978,J. Ultrastruct. Res., 65, 195), that the surface structure of the particulate membrane face is due predominantly to rhodopsin molecules forming a separate layer in the disk membrane. © 1979 Academic Press, Inc.