[FLuorescence of photoactive bacteriorhodopsin]

Area of Science:

• Biophysics
• Photochemistry
• Membrane Protein Spectroscopy

Context:

• Bacteriorhodopsin (BR) is a light-driven proton pump embedded in microbial membranes.
• Understanding BR's photochemistry is crucial for bioenergetics and optoelectronic applications.
• Fluorescence spectroscopy provides insights into the electronic states and dynamics of BR.

Purpose:

• To characterize the fluorescence properties of different bacteriorhodopsin (BR) states: all-trans-BR (BR570), 13-cis-BR (BR560), and the P585 intermediate.
• To investigate the photoactivation of fluorescence in BR states.
• To elucidate the relationship between fluorescence, absorption, and photoconversion pathways in BR.

Summary:

• Fluorescence spectra and excitation spectra were measured for BR570, BR560, and P585, showing maxima at 720-740 nm and 578-585 nm, respectively, correlating with absorption spectra.
• A significant increase in BR570 fluorescence quantum yield (photoactivation) was observed at -196°C, indicating a parallel photoprocess distinct from photoconversion.
• BR560 emission was not photoactivated, and other membrane-bound BR forms (B578, B630) exhibited higher fluorescence yields.

Impact:

• The findings suggest a model involving a common intermediate excited level for emission and photoconversion in BR.
• Identifies photoactivated BR570 as a distinct state, differing from previously described pseudo-BR.
• Provides a deeper understanding of BR's photophysical mechanisms, relevant for designing light-sensitive biomolecular systems.