Transbilayer distribution of phospholipid fatty acyl chains in photoreceptor membrane.

The transverse distribution of the fatty acyl chains of the major phospholipids over the two faces of the photoreceptor membranes has been determined in bovine rod outer segment (stacked disk) preparations. For this purpose, the fatty acid composition of the phospholipids has been analyzed before and after treatment with trinitrobenzenesulfonic acid and phospholipase D. The latter agents are used under conditions in which they have been demonstrated to attack only the outer (cytoplasmic) face of the membrane.

Transbilayer distribution of phospholipids in photoreceptor membrane studied with various phospholipases.

The distribution of the three major phospholipids of bovine rod outer segment disk membranes over the two faces of the membrane has been studied by means of treatment with phospholipase C, phospholipase A2 and phospholipase D. Two different preparations of rod outer segment disk membranes have been used, which are called 'stacked disks' and 'disk vesicles' on account of their morphological appearance. The hydrolysis patterns obtained by phospholipase treatment of these preparations have been compared to those of a retinal lipid suspension or detergent-solubilized disk membranes, which serve as control preparations with a similar phospholipid composition but a random availability of the phospholipids.

Transverse distribution of phospholipids in the vertebrate photoreceptor membrane.

A study has been made of the distribution of the three major phospholipids of the bovine photoreceptor membrane over the two faces of the lipid bilayer. Three different approaches have been used: a . Treatment of isolated intact outer segments and disk vesicles (lysed outer segments) with three different phospholipases and determination of the degradation pattern.

A possible role of rhodopsin in maintaining bilayer structure in the photoreceptor membrane.

31P-NMR measurements demonstrate that at 37 degrees C, independent of the photolytic state of the photopigment rhodopsin, the lipids in the photo-receptormembrane are almost exclusively organised in a bilayer. In strong contrast, the 31P-NMR spectra of the extracted lipids are characteristic for the hexagonal HII phase and an isotropic phase. The isotropic phase is characterised by freeze-fracture electron microscopy as particles and pits on smooth surfaces, possibly indicating inverted micelles.