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Abstract:
Besides the “classical” chromophores retinal (visual pigment: rhodopsin) and 3-dehydroretinal (visual pigment: porphyropsin), recently a new chromophore has been found in several insect groups: 3-hydroxyretinal (visual pigment: xanthopsin). Evolutionary aspects are considered — the first interaction of light with the photoreceptor must not necessarily take place at the Schiff base-linked chromophore. In many photoreceptors, e.g., of many fly species, light can be absorbed by a sensitizing pigment which then transfers energy (Förster mechanism) to the Schiff base-linked chromophore. This chromophore is then isomerized and leads to excitation of the receptor. The sensitizing pigment in higher flies is identified as 3-hydroxyretinol, and in one more primitive fly species (Simuliid) most likely as retinol. Functional consequences of sensitization are illustrated.
