ABSTRACT
Purple membranes (PMs) are violet distinct areas of the cytoplasmatic membrane of the extremely halophilic bacteria Halobacterium salinarium. PMs are built only by a single protein–bacteriorhodopsin, functioning as a photoinduced proton pump, converting the solar energy in a transmembrane proton gradient. In aqueous medium, PMs are not closed in vesicles and as a result the membrane electric asymmetry manifests itself as a permanent dipole moment. The optical function determines the magnitude of the electro-optical effect (EOE) for a certain degree of orientation. The relative EOE can be represented as a product of the orientational and optical functions. Rayleigh–Debye–Gans theory describes single scattering by optically independent particles. Particles with inhomogeneous composition, biological membranes in particular, can be considered as optically homogeneous, if all their elements have the same refractive index. The fact that electrostatic interactions in the membrane can change PM curvature allows assuming that a similar effect could be observed in an external field also.
