Photochemical conversion of the O-intermediate to 9-cis-retinal-containing products in bacteriorhodopsin films

Abstract

The photochemical activity of the O-state was investigated in bacteriorhodopsin (BR) films containing wildtype BR at pH 6.5 in the presence of glycerol. The formation of a photoproduct of O with an absorption maximum at 490 nm and 9-cis-retinal configuration was found. This 490-nm product was named P and shows a slow thermal reaction into a compound with a maximal absorption at 380 nm which was named Q and contains free 9-cis-retinal in the proteins binding site. The photoproducts of O, i.e., P and Q, are very similar, or even identical, to those previously observed in blue membranes. Common to the O-state and blue membrane forms of bacteriorhodopsin is a protonated aspartic acid 85, and we suggest that it is the reduced negative charge around the Schiff base which is responsible for the 9-cis photoisomerization. The release of a proton from aspartic acid 85 is linked to the conversion of the O-state back to the initial state of BR. Therefore the conditions of low proton mobility in BR films containing glycerol favor the accumulation of the O-state. For optical and holographic applications such BR films are very attractive. It is possible to create photoproducts with red light which are thermally stable at room temperature and that can be photochemically erased. Dependent on the light composition both properties can be realized in the same sample material. This feature may bridge the gap between information processing and short-term and long-term storage of information with BR.

Directed evolution of bacteriorhodopsin for applications in bioelectronics

“…This high quantum efficiency is identical to that of the visual photopigment, rhodopsin, which is found in the photoreceptor cells of the retina [68,69]. One of the unique features of the BR photocycle is the branched photocycle [25,[70][71][72]. During the classical photocycle of BR, the last and most red-shifted intermediate, designated as the O state, contains an all-trans configuration of the retinal chromophore ( figure 1).…”

Fluorescence spectra of bacteriorhodopsin and the intermediates O and Q at room temperature

“…The origin of the narrow spectrum was attributed The fluorescence spectrum of O was identical to that of the deionized (or acidified) purple membrane bR6o 5 (data not shown). It is reported that O and the all-trans component of bR605 (t-bR605) have common photochemical properties: the lack of the M-form in their photocycles [16,17] and the formation of 9-cis-retinal-containing photoproducts [18,19]. We found that the structure of O in the excited state is same as that of t-bR605.…”

Mechanism of voltage-sensitive fluorescence in a microbial rhodopsin

“…[The term "Q" state has been used to represent other intermediates in the BR photocycle (18). Here, we refer exclusively to the Ohtani Q.]…”

“…Although the photocycle was initially viewed as a series of sequential steps (13,14), kinetic evidence suggests rapid equilibrium among the states within the 13-cis manifold (15)(16)(17). Excitation of photocycle intermediates generates off-pathway states, some of which have been reported to be fluorescent (18)(19)(20)(21).…”