Linear dichroism of rhodopsin in air-water interface films

Abstract

Air-water interface films of purified cattle rhodopsin and defined phospholipids are formed by the osmotic lysis of reconstituted membrane vesicles. The interface films thus formed consist of a phospholipid monolayer containing vesicle membrane fragments. Rhodopsin molecules at the interface are restricted within the membrane fragments where they are spectrophotometrically intact and capable of undergoing photoregeneration and chemical regeneration. Multilayers of up to 8 layers can be built from these interface films. The visible absorption band of rhodopsin in these multilayers is linearly dichroic. Quantitative analysis of the linear dichroism reveals that the dipole moment of transition of the retinal chromophore in rhodopsin forms an angle of 15 degrees +/- 4 degrees with the plane of the membrane fragments in the interface film. This orientation of the chromophore relative to the plane of the membrane is essentially the same as that observed in the intact retina. Thus, the orientation of rhodopsin in the interface films is similar to that in the intact disc membranes.

Estimation of disk membrane lateral pressure and molecular area of rhodopsin by the measurement of its orientation at the nitrogen-water interface from an ellipsometric study

“…It follows that the surface pressure required to maintain the transmembrane orientation of rhodopsin, under our experimental conditions, is 38 mN/m. The results of Korenbrot and Jones (1979) support this conclusion. They have demonstrated that rhodopsin-phospholipid films transferred onto a hydrophilic glass support at this pressure (38 mN/m) show pigment orientation indistinguishable from that found in native disk membrane when examined by linear dichroism.…”

Supported phospholipid bilayers

“…The transfer of phospholipid monolayers onto hydrophilic substrates by a Langmuir-Blodgett technique has been attempted before (Levine et al, 1968), but has not found wide application in biophysical research compared with the numerous studies on fatty acid and soap films (for an excellent review see Kuhn et al, 1972). Korenbrot and co-workers (Korenbrot and Pramik, 1977;Korenbrot and Jones, 1979) have used Langmuir-Blodgett phospholipid films containing rhodopsin for structural and spectroscopic investigations. Langmuir-Blodgett films of phospholipids have also been used for device fabrication (Procarione and Kauffman, 1974;Taylor and Mahboubian-Jones, 1982).…”

Incorporation of photoreceptor membrane into a multilamellar film

“…Many methods have been reported for orienting biological membranes. These include the use of electric or magnetic fields (2,3), the deposition of membrane sheets on a substrate by successive dipping through an air/water interface (4,5), surfactant coated surface induced orientation (6), drying (7), and centrifugation (8). It is however, sometimes difflcult to make quantitative measurements with such membrane preparations due to poor orientation, light scattering, optical inhomogeneities, insufficient thickness of the sample, or thickness variations.…”