“…To summarize the main features of the photoisomerization, it is, firstly, highly sensitive and efficient: ~70% of the all-trans precursor can be photoisomerized by irradition of the fly with 410-430 nm light, at <1014 photons cm-~.s -~ for 1 h. Secondly, the formation of photoproduct, the 11-c/s isomer, is highly specific. Finally, the peak of the action spectrum of the photoisomerization shifts to a wavelength some 30-40 nm longer than the absorption maximum of the free all-trans 3-hydroxyretinal (386 nm in chloroform; Mayer and Santer, 1980). It is strongly suggested that the precursor, 3-hydroxyretinal, is bound to a specific binding protein, as is the case for the retinal-based pigment systems, such as the retinochrome in the cephalopod retina (Hara and Hara, 1972) or retinal-binding proteins in the honeybee retina (Pepe et al, 1976).…”