Photochemistry in dried polymer films incorporating the deionized blue membrane form of bacteriorhodopsin

Jack R. Tallent, Jeffrey A. Stuart, Q. Wang Song, Edward J. Schmidt, Charles H. Martin, Robert R. Birge

Research output: Contribution to journalArticlepeer-review

30 Scopus citations

Abstract

The preparation and photochemical properties of dried deionized blue membrane (dlbR600; λ(max) ≃ 600 nm, ε ≃ 54, 760 cm-1 M-1, f ≃ 1.1) in polyvinyl alcohol films are studied. Reversible photoconversion from dlbR600 to the pink membrane (dlbR485; λ(max) ≃ 485 nm) is shown to occur in these films under conditions of strong 647-nm laser irradiation. The pink membrane analog, dlbR485, has a molar extinction coefficient of ~39,000 cm-1 M-1 (f ≃ 1.2). The ratio of pink → blue and blue → pink quantum efficiencies is 33 ± 5. We observe an additional blue-shifted species (dlbR455, λ(max) ≃ 455 nm) with a very low oscillator strength (f ≃ 0.6, ε ≃ 26,000 cm-1 M-1). This species is the product of fast thermal decay of dlbR485. 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 ~6 kcal mol-1 while increasing the corresponding all-trans → 13-cis barrier to ~4 kcal mol-1. Photochemical formation of both 9-cis and 13-cis photoproducts are now competitive, as is observed experimentally. We suggest that dlbR455 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 λ(max) absorption band.

Original languageEnglish (US)
Pages (from-to)1619-1634
Number of pages16
JournalBiophysical Journal
Volume75
Issue number4
DOIs
StatePublished - Oct 1998

ASJC Scopus subject areas

  • Biophysics

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