Photochemistry in Dried Polymer Films Incorporating the Deionized Blue Membrane Form of Bacteriorhodopsin

Abstract

The preparation and photochemical properties of dried deionized blue membrane (dIbR600; lambdamax approximately 600 nm, epsilon approximately 54, 760 cm-1 M-1, f approximately 1.1) in polyvinyl alcohol films are studied. Reversible photoconversion from dIbR600 to the pink membrane (dIbR485; lambdamax approximately 485 nm) is shown to occur in these films under conditions of strong 647-nm laser irradiation. The pink membrane analog, dIbR485, has a molar extinction coefficient of approximately 39,000 cm-1 M-1 (f approximately 1.2). The ratio of pink --> blue and blue --> pink quantum efficiencies is 33 +/- 5. We observe an additional blue-shifted species (dIbR455, lambdamax approximately 455 nm) with a very low oscillator strength (f approximately 0.6, epsilon approximately 26,000 cm-1 M-1). This species is the product of fast thermal decay of dIbR485. Molecular modeling indicates that charge/charge and charge/dipole interactions introduced by the protonation of ASP85 are responsible for lowering the excited-state all-trans --> 9-cis barrier to approximately 6 kcal mol-1 while increasing the corresponding all-trans --> 13-cis barrier to approximately 4 kcal mol-1. Photochemical formation of both 9-cis and 13-cis photoproducts are now competitive, as is observed experimentally. We suggest that dIbR455 may be a 9-cis, 10-s-distorted species that partially divides the chromophore into two localized conjugated segments with a concomitant blue shift and decreased oscillator strength of the lambdamax absorption band.

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).…”

Crystal Structures of Acid Blue and Alkaline Purple Forms of Bacteriorhodopsin

“…These absorption changes can be explained by formation of a K-like red-shifted intermediate and its reverse photoreaction, respectively. 35 Although the 9-cis isomer (l max Z455 nm) has been reported to be produced by illumination of acid blue membrane at ambient temperature, 36,37 there was no indication for production of the 9-cis isomer in the P622 crystal at 100 K.…”

Optimization of bacteriorhodopsin production by Halobacterium salinarium PTCC 1685

“…H. salinarium synthesize the purple membrane when dissolved oxygen concentrations become too low to sustain aerobic ATP production in the presence of light [11,12]. The production of the purple membrane allows the organism to switch from oxidative phosphorylation to photosynthesis as a means of energy production [13,14]. H. salinrium has most frequently been employed for the production of bacteriorhodopsin.…”