[Molecular interactions in the membranes of visual photoreceptors. Study using mixed monomolecular film].
We have examined the interactions in a mixed monomolecular film between the 11-cis and all-trans isomers of retinal and different saturated and unsaturated phosphatidylcholines and phosphatidylethanolamines. The phase diagrams of the different binary mixtures are drawn using the surface pressure isotherms measured on 10(-3) M phosphate buffer at 21 +/- 1 degree C. Analysis of the results shows that the unsaturated chain phospholipids (dioleoyl L-phosphatidylcholine and dioleoyl L-phosphatidylethanolamine extracted from bovine retinas) and the retinal isomers are miscible at the interface. In addition, the excess free energies of mixing are identical for these mixtures. On the other hand, the saturated phospholipids (distearoyl L-phosphatidylcholine and distearoyl L-phosphatidylethanolamine) are not miscible with the retinal isomers under the same conditions. The comparison between the results obtained with the saturated lipid and unsaturated lipid mixtures shows the importance of hydrophobic forces in the thermodynamics of the interactions of these systems. In addition, the isotherms of the mixtures containing phosphatidylethanolamine do not vary with the pH of the subphase in the region studied, pH 5.5 to 8.2. These results raise serious doubts about the existence of a Schiff base between phosphatidylethanolamine and the retinals at the interface. The possible implications of this phenomenon for the disc membrane are analyzed, particularly with respect to the stability of the retinals in vivo.
D000818:Animals; D002417:Cattle; D002462:Cell Membrane / Q000502:physiology; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D010786:Photoreceptor Cells / Q000502:physiology*; D011312:Pressure; D012172:Retinaldehyde; D012176:Retinoids; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013499:Surface Properties; D013816:Thermodynamics
D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D012176:Retinoids; D012172:Retinaldehyde
Les interactions moléculaires dans les membranes des photorécepteurs visuels. Etude en film monomoléculaire mixte.