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The Photocycles of Bacteriorhodopsin
Author(s) -
Lanyi Janos K.,
Váró György
Publication year - 1995
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.199500037
Subject(s) - bacteriorhodopsin , chemistry , photoisomerization , protonation , schiff base , proton , proton transport , photochemistry , picosecond , halobacteriaceae , stereochemistry , isomerization , ion , membrane , halobacterium salinarum , biochemistry , organic chemistry , laser , physics , quantum mechanics , optics , catalysis
The photoisomerization of all‐ trans ‐retinal of bacteriorhodopsin to 13‐ cis gives rise to a series of unstable states that thermally interconvert on the picosecond to millisecond timescale, and ultimately decay back to the initial state. Since this “photocycle” drives the translocation of a proton from the cytoplasmic to the extracellular side of the membrane, its detailed description is essential to understand the mechanism of the ion transport. The interconversions of the intermediates of the cycle, K 610 , L 550 , M 410 , N 560 , and O 640 , proceed with complex multiphasic kinetics, and there is much disagreement over the interpretation of this. However, many groups have described the photocycle as a single reaction sequence with several reversible reactions, some pH‐dependent. Through the use of time‐resolved spectroscopy and site‐specific mutations, such a scheme provides a reasonable model for how the retinal Schiff base first transfers its proton to Asp‐85, followed by release of a proton to the extracellular side; then the Schiff base is reprotonated from Asp‐96, and proton uptake from the cytoplasmic surface restores the initial protonation state of Asp‐96, while the retinal reisomerizes to all‐ trans.