Energy transfer in spectrally inhomogeneous light-harvesting pigment-protein complexes of purple bacteria

Summary, in English

Energy transfer within the peripheral light-harvesting antenna of the purple bacteria Rhodobacter sphaeroides and Rhodopseudomonas palustris was studied by one- and two-color pump-probe absorption spectroscopy with approximately 100-fs tunable pulses at room temperature and at 77 K. The energy transfer from B800 to B850 occurs with a time constant of 0.7 +/- 0.05 ps at room temperature and 1.8 +/- 0.2 ps at 77 K and is similar in both species. Anisotropy measurements suggest a limited but fast B800 <--> B800 transfer time (tau approximately 0.3 ps). This is analyzed as incoherent hopping of the excitation in a system of spectrally inhomogeneous antenna pigment-protein complexes, by a master equation approach. The simulations show that the measured B800 dynamics is well described as energy transfer with a characteristic average nearest-neighbor pairwise transfer time of 0.35 ps among approximately 10 Bchl molecules in a circular arrangement, in good agreement with the recent high-resolution structure of LH2. The possible presence of fast intramolecular relaxation processes within the Bchl a molecule was investigated by measurement of time-resolved difference absorption spectra and kinetics of Bchl a in solution and in low-temperature glasses. From these measurements it is concluded that fast transients observed at room temperature are due mainly to solvation processes, whereas at 77 K predominantly slower (> 10-ps) relaxation occurs.

• Author: S. Hess; E. Åkesson; R. J. Cogdell; T. Pullerits; V. Sundström
• Department/s: Chemical Physics
• Publishing year: 1995
• Language: English
• Pages: 2211-2225
• Publication/Series: Biophysical Journal
• Volume: 69
• Issue: 6
• Links: http://dx.doi.org/10.1016/S0006-3495(95)80137-2
• Document type: Journal article
• Publisher: Cell Press
• Topic: Biophysics
• Status: Published
• ISBN/ISSN/Other: ISSN: 0006-3495