Trapping of a long-living charge separated state of photosynthetic reaction centers in proteoliposomes of negatively charged phospholipids

Reaction centers from the purple bacterium Rhodobacter sphaeroides strain R-26.1 were purified and reconstituted in proteoliposomes formed by the anionic phospholipids phosphatidylglycerol, phosphatidylserine and phosphatidylinositol and by the zwitterionic phospholipid phosphatidylcholine by size-exclusion chromatography in the dark and under illumination. We report the large stabilizing effect induced by anionic phospholipids on the protein charge separated state which results trapped in a long-living (up to tens of minutes) state with a yield up to 80%. This fully reversible state is formed in oxygenic conditions regardless the presence of the secondary quinone Q(B) and its lifetime and relative yield increase at low pH. In proteoliposomes formed with Q(A)-depleted reaction centers (RCs) the resulting protein is very light-sensitive and the long living charge separated state is not observed. The data collected in negatively charged proteoliposomes are discussed in terms of the electrostatic effect on the primary quinone acceptor and compared with similar long living species reported in literature and obtained in anionic, zwitterionic, and non-ionic detergents.