Surface-Enhanced Infrared Absorption Spectroscopy (SEIRAS) of Light-Activated Photosynthetic Reaction Centers from Rhodobacter sphaeroides Reconstituted in a Biomimetic Membrane System

Surface-enhanced IR absorption spectroscopy (SEIRAS) in the ATR configuration has been performed on reaction centers (RCs) from R. sphaeroides. Surface-enhancement is achieved by a thin, structured gold film present on the surface of an ATR crystal. Purified RCs are immobilized as a monolayer on top of the gold film via a poly his-tag engineered to the C-terminal end of the M subunit. Subsequently, the RCs are reconstituted into a lipid bilayer by in situ dialysis. Light-minus-dark absorbance spectra were recorded under continuous illumination using the spectrum in the dark as the reference. A number of strong bands have been observed indicating the excitation of the special pair as well as alterations of quinone/quinol species. Spectra were recorded at different time intervals with and without liposoluble Q10 coreconstituted into the lipid phase. A steady (photostationary) state was approached slowly and bands were found to increase or decrease reversibly on illumination and relaxation. Tentative assignm...