3.E.2.1.1
Photosynthetic reaction center (RC).  Chromatophores containing the RC and light harvesting complex, LH1, can interface with a conducting support to allow capture and conversion of solar energy as an alternative fuel source (Harrold et al. 2013). This RC may catalyze transmembrane electron transfer, as for members of TC class 5 (Khatypov et al. 2017). Cytochrome bc1 and the reaction centre complex are in proximity in live Rhodobacter sphaeroides cells (Vasilev et al. 2021).  Dipyridamole (DIP) alters the efficiency of energy transfer from the light-harvesting complex LH2 to the LH1-reaction center core complex and to produce the long-wavelength ("red") shift of the absorption band of light-harvesting bacteriochlorophyll molecules in the IR spectral region at 840-900 nm (Knox et al. 2022). This shift is associated with the membrane transition to the energized state. DIP reduces the photooxidized bacteriochlorophyll of the reaction center, which accelerated electron flow along the electron transport chain, thereby stimulating generation of the transmembrane potential on the chromatophore membrane (Knox et al. 2022).  Tools for analyzing protonation states and for tracing proton transfer pathways have been developed with examples from the Rb. sphaeroides photosynthetic reaction centers (Wei et al. 2023).