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Optical picosecond studies of bacteriorhodopsin containing a sterically fixed retinal

Authors
Journal
Biochimica et Biophysica Acta (BBA) - Bioenergetics
0005-2728
Publisher
Elsevier
Publication Date
Volume
767
Issue
3
Identifiers
DOI: 10.1016/0005-2728(84)90065-3
Keywords
  • Bacteriorhodopsin
  • Retinal Analogue
  • Picosecond Spectroscopy
  • Proton Pump
Disciplines
  • Biology
  • Chemistry
  • Physics

Abstract

Abstract The photochemical behaviour of an analogous bacteriorhodopsin (9,12-Ph-BR) which contains the sterically fixed 9,12-phenylretinal has been investigated with picosecond spectroscopy. The following results have been obtained. No ground-state intermediate photoproduct is found in agreement with the previous observation that 9,12-Ph-BR does not exhibit proton pumping under illumination. The excited singlet state has a lifetime of τ S = 10 ± 2 ps. This lifetime agrees favourably with the value calculated from the radiative lifetime τ rad = 6.2 ns and the fluorescence quantum efficiency of 1.2·10 −3. Excited-state absorption occurs which results in fluorescence in the ultraviolet region. These various observations differ drastically from the corresponding findings on bacteriorhodopsin. Most important for an understanding of the differences is the fact that 9,12-phenylretinal does not isomerize in the protein's binding site in contrast to retinal. Our data therefore suggest that the formation of the intermediate K observed in bacteriorhodopsin is accompanied by the all- trans to 13- cis isomerization.

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