Energy transfer within the isolated light-harvesting B800–850 pigment-protein complex of Rhodobacter sphaeroides

We have used picosecond absorption spectroscopy with low intensity (5 · 10¹¹–5 · 10¹² photons · pulse⁻¹ · cm⁻²) continuously tunable infrared (800–900 nm) pulses to study the energy transfer dynamics in the isolated B800–850 pigment-protein complex of Rhodobacter sphaeroides. Our results suggest the following picture of the energy transfer dynamics: (i) a fast transfer, within approx. 1 ps, from BChl 800 to BChl 850; (ii) transfer among different BChl 800's with a rate which is at the most of the same order of magnitude as that of BChl 800 → BChl 850 transfer; (iii) very fast transfer (k > 1 · 10¹² s⁻¹) between BChl 850 molecules. Assuming Förster type of energy transfer maximum distances of about 22 and 15 Å are obtained for the BChl 800–BChl 850 and BChl 850–BChl 850 separations, respectively.