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THE UV PROTEIN FLUORESCENCE OF PURPLE MEMBRANE AND ITS APOMEMBRANE
Author(s) -
Acuña A. U.,
González J.,
Lillo M. P.,
Otón J. M.
Publication year - 1984
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1984.tb04598.x
Subject(s) - membrane , fluorescence , chemistry , bacteriorhodopsin , molecule , photochemistry , monomer , fluorescence anisotropy , quenching (fluorescence) , biophysics , crystallography , polymer , biochemistry , organic chemistry , biology , physics , quantum mechanics
The ultraviolet fluorescence of the purple membrane of H. halobium and its apomembrane was characterized by measuring emission spectra, polarization, decay lifetimes and the changes induced by pH and temperature. The fluorescence quantum yields of the two membranes are 0.024 × 0.003 and 0.17 × 0.03, respectively. The emission, which shows lifetimes in the 0.4 to 4 ns range, was assigned to heterogeneous populations of emitters, consisting, probably, of two tryptophans in the purple membrane and seven or eight residues in the apomembrane. Acrylamide quenching experiments showed that the accessibility of this neutral quencher to the fluorophors is reduced greatly in both membranes. Fluorimetric methods were also used in an attempt to monitor the purple complex reconstitution process. It was concluded that the fluorescence quantum yields of any monomers, dimers and trimers present in the partially reconstituted membranes should be very similar. Finally, based on the spectroscopic results and on specific folding patterns of the seven α‐helical regions of bacteriorhodopsin (Stoeckenius and Bogomolni, 1982), it is proposed that Trp 137, Trp 138 (and perhaps Trp 10) of the protein molecule are the most plausible fluorophors in the purple membrane. It is also suggested that the protein in the apomembrane takes a more open configuration which is permeable to small ions and molecules.