Singlet oxygen generation in the reaction centers of Rhodobacter sphaeroides.

Singlet oxygen (1O2) generation in the reaction centers (RCs) of Rhodobacter sphaeroides wild type was characterized by luminescent emission in the near infrared region (time resolved transients and emission spectra) and quantified to have quantum yield of 0.03 +/- 0.005. 1O2 emission was measured as a function of temperature, ascorbate, urea and potassium ferricyanide concentrations and as a function of incubation time in H2O:D2O mixtures. 1O2 was shown to be affected by the RC dynamics and to originate from the reaction of molecular oxygen with two sources of triplets: photoactive dimer formed by singlet-triplet mixing and bacteriopheophytin formed by direct photoexcitation and intersystem crossing.