Photostable pigments within the membrane of photoreceptors and their possible role.

In the majority of ommatidia of the fly, the membrane of the central rhabdomere contains--besides the rhodopsin--a photostable pigment. Due to its selective absorption in the blue spectral range, this pigment (possibly a carotene) could modify the spectral senstivity of the central receptor cells. It furthermore may change the fluidity of the microvillus membrane and hence affect the alignment of rhodopsin molecules. Indirect evidence for a possible role of the photostable pigment as an "antenna" -pigment for rhodopsin is discussed.