Reason for the lack of light‐dark adaptation inpharaonis phoborhodopsin: reconstitution with 13‐cis‐retinal

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Abstract
The reconstitution ofpharaonis phoborhodopsin was performed by incubation of its opsin with 13-cis-retinal. Spectrum change was very slow, and two phases of the change were observed: the first and second phases are due to the transient formation of 13-cis pigment and spontaneous isomerization toall-trans-retinal, respectively. Slow binding supports an idea that the retinal binding pocket of ppR is highly restricted. Being bent in the configuration, 13-cis-retinal cannot be accommodated in the pocket due to the steric hindrance. This is a possible reason for the lack of light-dark adaptation