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Thermal Recovery of Iodopsin from Photobleaching Intermediates †
Author(s) -
Imamoto Yasushi,
Shichida Yoshinori
Publication year - 2008
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.2008.00332.x
Subject(s) - isomerization , photobleaching , chromophore , chemistry , steric effects , photochemistry , molecule , crystallography , stereochemistry , organic chemistry , fluorescence , catalysis , optics , physics
The chloride effect on the photobleaching process of iodopsin, a chicken red‐sensitive cone visual pigment, was studied in detail by time‐resolved low‐temperature spectroscopy at −40°C to −10°C. Decay‐associated difference spectra obtained by kinetic analysis using the singular value decomposition method were composed of spectra of BL‐iodopsin, lumiiodopsin, metaiodopsin I, metaiodopsin II and metaiodopsin III, essentially identical to those at room temperature. In each conversion step however, iodopsin was partially regenerated, which is not observed in the bleaching process for other visual pigments or iodopsin at room temperature. Moreover, iodopsin was slowly regenerated from the bleached species. The reverse reactions were completely suppressed by substitution of lyotropic NO 3 − for Cl − , suggesting that Cl − binding to iodopsin interferes with light‐induced cis – trans isomerization of the chromophore. It is likely that the water molecule hydrating Cl − forms the additional hydrogen bond(s), by which the protein conformational change necessary to release this steric hindrance becomes enthalpic. As progress of the bleaching process is a consequence of protein conformational change, it is suppressed at low temperatures, resulting in thermal back‐isomerization.

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