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THEORY OF THE OPTICAL ABSORPTION OF LIGHT‐ADAPTED BACTERIORHODOPSIN AND ITS ACIDIFIED FORMS
Author(s) -
Yoshihara Toru,
Suzuki Hideo,
Maeda Akio
Publication year - 1981
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.1751-1097.1981.tb05452.x
Subject(s) - bacteriorhodopsin , chromophore , chemistry , protonation , absorption (acoustics) , halobacteriaceae , photochemistry , absorption spectroscopy , schiff base , ion , crystallography , physics , optics , organic chemistry , biochemistry , halobacterium salinarum , membrane
Abstract— We assume a model for bacteriorhodopsin chromophore such that the protonated retinal Schiff‐base (PRSB) interacts with two anions in the case of light‐adapted bacteriorhodopsin (bR L ), while it does with one anion in the case of the acidified form of bacteriorhodopsin (bR acid 600 ). On the basis of this model, the π‐electronic states of all‐ trans ‐PRSB are calculated according to our LCAO‐ASMO‐SCF‐CI method, the anions being approximated by negative point‐charges in the plane of PRSB π‐system. A possible distribution of the negative point‐charges around PRSB is proposed for the chromophores of bR L , bR acid 600 , and the two irradiated forms of bR acid 600 (the one at 3°C containing 9‐ cis ‐PRSB, and the other at — 72°C all‐ trans ‐PRSB). It is shown that the wavelength λ max of absorption maximum observed for each form of bacteriorhodopsin can be explained reasonably well by the suggested charge distribution. Furthermore, a model for the structure of the active site of bR L is proposed, considering that two COO − groups form the anions that interact with PRSB. The calculated optical absorption of all‐ trans ‐PRSB at such a site is shown to be consistent with the observed absorption spectrum of bR L .