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ISOMERIZATION OF THE RETINYLIDENE CHROMOPHORE OF BACTERIORHODOPSIN IN LIGHT ADAPTATION: INTRINSIC ISOMERIZATION OF THE CHROMOPHORE AND ITS CONTROL BY THE APO‐PROTEIN
Author(s) -
Koyama Yasushi,
Nakasu Hiroaki,
Mukai Yumiko,
Tokunaga Fumio
Publication year - 1993
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.1751-1097.1993.tb02946.x
Subject(s) - photostationary state , chromophore , bacteriorhodopsin , isomerization , photochemistry , photoisomerization , chemistry , rhodopsin , retinal , halobacteriaceae , organic chemistry , biochemistry , halobacterium salinarum , membrane , catalysis
— The dependence of the isomeric configuration of the retinylidene chromophore of bacteriorhodopsin on the pH value and on the wavelength of irradiation (in a photostationary state) were examined by high performance liquid chromatographic analyses of extracted retinal. The process of isomerization of the chromophore during light adaptation was also traced. More than 93% of all‐ trans and less than 5% of 13‐ cis retinal were extracted in the photostationary state for irradiation at 560 nm in the pH region of5–9 as well as for irradiation in the wavelength region of 400–650 nm at pH 7. Comparison of the above photostationary state composition with that of protonated n ‐butylamine Schiff base of retinal indicates that strong constraint is applied to the chromophore by the apo‐protein. The constraint can be changed at low or high pH by a partial denaturation or transition of the apo‐protein, which results in the generation of 11‐ cis retinal in the extract. At higher photon density, the isomerization process of the chromophore during light adaptation at pH 7 was characterized, as extracted isomeric retinal, by (1) the initial decrease in 13‐ cis and increase in all‐ trans , (2) a subsequent, transient toward the above photostationary state composition. The results are discussed in terms of both the photoisomerization pattern inherent in the retinylidene chromophore and the control by the apo‐protein.