Effects of visual pigments on the organization of phospholipid multibilayer model membranes--a spin probe study

A cholestane spin probe was used to study the effects of the all-trans isomers of retinal and retinol, and the 13-cis- isomer of retinal on the degree of organization of oriented phospholipid multibilayer model membranes in the dark. Concentration-dependent effects were observed indicative of changes in the degree of organization of phosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl serine, sphingomyelin, and brain lipids. In general the all-trans compounds improved the degree of order of the lipid films at low concentrations, and decreased it at high concentrations. The 13-cis retinal served only to decrease the degree of order. The magnitudes of these effects depend on lipid composition and the nature of the pigment polar residue. Chemical as well as nonbonding interactions are considered to be responsible for these various effects.