1: Biophys J  1985 Jan;47(1):43-54 

Excited-state dynamics of bacteriorhodopsin.

Kouyama T, Kinosita K Jr, Ikegami A.

Near infrared emission of bacteriorhodopsin at neutral pH and at room
temperature was characterized by a large Stokes shift. This characteristic was
lost in an acidic pH (approximately pH 2) where a remarkable enchancement (more
than 10 times) in the fluorescence quantum yield accompanied the red shift in
the main absorption band. It is suggested from fluorescence polarization
measurements that the emission occurs from the first allowed excited state of
the retinylidene chromophore, irrespective of pH. We suggest that the large
Stokes shift observed at neutral pH is a result of a charge displacement (e.g.,
proton translocation) that occurs immediately after excitation, and is prevented
by protonation (in the ground state) of an amino-acid residue in the protein.

PMID: 3978189 [PubMed - indexed for MEDLINE]