The senitizing pigment in fly photoreceptors: Properties and candidates

Many lines of evidence suggest that the ultraviolet (uv) sensitivity found in the most common photoreceptor class in the fly is due to a sensitizing pigment which transmits the energy of absorbed light quanta to the visual pigment (Kirschfeld et al. 1977). It is shown that the uv extinction of the rhabdomeres has a vibrational fine structure corresponding to that found in the receptors' spectral sensitivity (Gemperlein et al. 1980). The uv extinction is greatly reduced when flies are reared on a carotenoid-deficient diet, in which case the vibrational fine structure in sensitivity is also lost. Properties (extinction, fluorescence) of several groups of substances that could represent the sensitizing pigment are illustrated