Increasing the Rate of Energy Transfer between the LHI Antenna and the Reaction Center in the Photosynthetic Bacterium Rhodobacter sphaeroides

Energy transfer from Rhodobacter sphaeroides light-harvesting complex I (LHI) to the reaction center (RC) was investigated with steady-state and time-resolved fluorescence spectroscopy. Chromatophores isolated from a strain containing LHI with the mutation αTrp43 to Phe (LHI mutant) and strains containing either the LHI mutant with wild-type RCs (LHI mutant + WT RC) or the LHI mutant with the RC mutations LH-(L131)+LH(M160)+FH(M197) (LHI mutant + T1 RC) were investigated at 294 and 77 K. In the LHI mutant, absorption and fluorescence spectra were blue-shifted by 21 nm compared to wild-type LHI. The energy transfer from mutated LHI to the RC occurs about two times faster than energy transfer from wild-type LHI to the RC. The acceleration of energy transfer is consistent with the increase in the energy transfer rate estimated from the spectral overlap between the RC absorbance and the LHI fluorescence according to Förster energy transfer theory.