Rhodobacter spheroides RCs (M252V mutant which does not assemble with QA) were isolated as previously described. The protein was stored in 10 mM Tris (pH 8.0), containing 0.03% (w/v) LDAO. For reconstitution, a film was prepared in a glass vial by evaporating solvents from 80 µL of 5 mg/mL solution of PG2 in 1:1 CHCl3:MeOH. The vial was kept in the desiccator for 12 h. The film was hydrated by gently tapping with 400 µL of a solution consisting of 10 mM Tris (pH 8.0), 30 mM octyl glucoside, 0.26 mM LDAO, and 6 µM RC. The protein to GDGT lipid ratio was about 1:100. The lipid/detergent/protein mixture was added to 18 mg of pre-cleaned wet BioBeads SM-2 resin (soaked in Milli-Q water) and allowed to tumble for 30 min at RT. Afterwards, the solution was separated from the beads and taken in a 10 kDa MWCO dialysis cassette. Dialysis was carried out against 10 mM Tris buffer (pH 8.0) for 48 h with 2 changes of buffer in between and a clear light purple dispersion is collected. Removal of detergents was verified by mass spectrometry. Transient (fs/ps) absorption spectroscopy measurements for RCs shown in Figure were obtained in the laboratory of Professor Dewey Holten and Christine Kirmaier by Dr. Kaitlin Faries at Washington University using previously described methods. We are indebted to them for providing this data.