Excitation energy transfer in Rhodopseudomonas sphaeroides chromatophore membranes fused with liposomes

The role of phospholipid in the structural organization of the light-harvesting complexes of Rhodopseudomonas sphaeroides was examined in photosynthetic (chromatophore) membrane vesicles fused with liposomes. Photochemically active preparations with progressive phospholipid enrichment up to greater than 15-fold were obtained by both polyethylene glycol- and acidic-pH-induced fusion. Their fluorescence emission at approximately 300 and 77 K was increased by 2-3.5-fold from the peripheral B800-850 antenna relative to that from the core B875 antenna. Up to 30-40% reduction in the efficiency of excitation energy transfer between B850 and B875 was also observed at 77 K suggesting a selective, phospholipid-induced dissociation of a portion of the B800-850 from the rest of the light-harvesting system.