artificial pigments of bacteriorhodopsin (bR) were synthesized with naphthylretinal [Np-retinal; (all-E-3-methyl-7-(2-naphthyl)-2,4,6-octatrienal] and termed Np-bR442, Np-bR503, and Np-bR480after their λmax’s. Although both Np-bR442and Np-bR503have the same all-trans-naphthylretinal binding to the same position of apoprotein as the native one, they are different in color and CD spectra, probably due to different steric interactions at the ring portion [Iwasa, T., Takao, M., Yamada, M., Tsujimoto, T., & Tokunaga, F. (1984) Biochemistry 23, 838–843]. Upon irradiation at room temperature, Np-bR480is produced from Np-bR442but not from Np-bR503. Np-bR480has a larger amount of 13-cis-retinal as its chromophore (60%) and reverts to Np-bR442in the dark at room temperature. Np-bR442and Np-bR503formed their own batho intermediates, which were photoreversibly converted to their mother pigments at -185 °C. Meta intermediates were formed from both pigments upon irradiation at -65 °C. The meta intermediate of Np-bR503disappeared at lower temperatures than that of Np-bR442and reverted to Np-bR503upon warming, while that from Np-bR442was converted to Np-bR480. These results indicate that the main photochemical reaction pathway is not disturbed by the substitution of a naphthyl group in place of a β-ionone ring or by the difference in the chromophoric structures around the ring portion.
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