Abstract
Inter-protein reactions of photosynthetic reaction centers (RCs) with bc1 complexes from R. sphaeroides, have been investigated using surface-enhanced Infrared-absorption spectroscopy (SEIRAS). Surface enhancement was achieved by a nano-structured gold surface. The proteins were immobilized via his-tags attached to the P side of the RC and the C-terminal end of the cytochrome (cyt) b subunit and co-reconstituted into a lipid bilayer by in-situ dialysis. In this configuration, the cyt c binding site of the two proteins is located on opposite sides of the membrane. Light-minus-dark absorbance spectra under continuous illumination in the absence of an electron donor indicated a slow quinone/semiquinone exchange, allowing release of ubiquinol (QH2) into the membrane. The interaction of the bc1 with QH2 was indicated by the stationary state obtained but only in the presence of cyt c. The interaction is discussed in terms of a semiquinone species formed in the course of the Q cycle mechanism of the bc1.
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