Photochemistry in dried polymer films incorporating the deionized blue membrane form of bacteriorhodopsin.
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.
Tallent
J R
JR
Department of Chemistry and W. M. Keck Center for Molecular Electronics, Syracuse University, Syracuse, New York 13244-4100 USA.
Stuart
J A
JA
Song
Q W
QW
Schmidt
E J
EJ
Martin
C H
CH
Birge
R R
RR
D000595:Amino Acid Sequence; D019843:Archaeal Proteins; D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000528:radiation effects; D001665:Binding Sites; D002338:Carotenoids; D025602:Halorhodopsins; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D010777:Photochemistry / Q000379:methods; D011487:Protein Conformation; D011789:Quantum Theory; D025603:Sensory Rhodopsins; D013053:Spectrophotometry / Q000295:instrumentation / Q000379:methods
D019843:Archaeal Proteins; D025602:Halorhodopsins; D025603:Sensory Rhodopsins; C061508:sensory rhodopsin II protein, archaeal; D002338:Carotenoids; D001436:Bacteriorhodopsins