Spectral and kinetic properties of semiquinones in bacterial photosynthetic reaction centres embedded in liposomes obtained by different phospholipds

Reaction centres (RC) isolated from the purple non-sulphur photosynthetic bacterium Rhodobacter sphaeroides have been reconstituted in different biomimetic systems (liposomes) prepared with three phospholipids, namely phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylglycerol (PG). The two quinones embedded in the protein have been selectively reduced by photo-activation in the presence of exogenous electron donor. The lifetimes of both semiquinones have been recorded along with their transient optical spectra. The spectra of the two semiquinones, markedly different in the infrared region, show only minor difference in the various solubilizing environments tested. On the other hand, the lifetimes were found to be sensibly reduced in the case of PG liposomes.