Probing for the threshold energy for visual transduction: red-shifted visual pigment analogs from 3-methoxy-3-dehydroretinal and related compounds.
While azulenic retinal analogs failed to yield a red-shifted visual pigment analog, the 9-cis isomers of the push-pull polyenals 3-methoxy-3-dehydroretinal and 14F-3-methoxy-3-dehydroretinal yielded iodopsin pigment analogs with absorption maxima at, respectively, 663 and 720 nm. The former gave a relatively stable batho product (700 nm) and was able to activate transducin. A lower activity was observed for the latter. One possible explanation for the combined results is that the excitation energies of these red-shifted pigments are approaching the threshold energy for visual transduction (although at this time we cannot rigorously exclude a role of the added F-atom in reducing the transducin activity).
Department of Biophysics, Graduate School of Science, Kyoto University, Japan.
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Imai
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Hirano
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Terakita
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Shichida
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Muthyala
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Chen
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Colmenares
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Liu
D012168:Retinal Pigments; D012172:Retinaldehyde / Q000031:analogs & derivatives*; D015398:Signal Transduction; D014785:Vision, Ocular
D012168:Retinal Pigments; D012172:Retinaldehyde