Fluorescence spectral fluctuations of single LH2 complexes from Rhodopseudomonas acidophila strain 10050.

We have investigated the energy landscape of the bacterial photosynthetic peripheral light-harvesting complex LH2 of purple bacterium Rhodopseudomonas acidophila by monitoring sequences of fluorescence spectra of single LH2 assemblies, at room temperature, with different excitation intensities as well as at elevated temperatures, utilizing a confocal microscope. The fluorescence peak wavelength of individual LH2 complexes was found to abruptly move between quasi-stable levels differing by up to 30 nm. These spectral shifts either to the blue or to the red were accompanied by a broadening and decrease of the intensity of the fluorescence spectrum. The frequency and size of these fluorescence peak movements were found to increase linearly with excitation intensity. Using the modified Redfield theory, changes in the realization of the static disorder accounted for the observed changes in spectral shape and intensity. Long lifetimes of the quasi-stable states suggest large free energy barriers between the different realizations.

[1]  Klaus Schulten,et al.  Photosynthetic apparatus of purple bacteria , 2002, Quarterly Reviews of Biophysics.

[2]  Graham R. Fleming,et al.  On the Mechanism of Light Harvesting in Photosynthetic Purple Bacteria: B800 to B850 Energy Transfer , 2000 .

[3]  N. Isaacs,et al.  The purple bacterial photosynthetic unit , 1996, Photosynthesis Research.

[4]  N. Isaacs,et al.  Studies on the light-harvesting complexes from the thermotolerant purple bacterium Rhodopseudomonas cryptolactis , 1995, Photosynthesis Research.

[5]  S. Mukamel,et al.  Exciton-migration and three-pulse femtosecond optical spectroscopies of photosynthetic antenna complexes , 1998 .

[6]  N. W. Isaacs,et al.  Crystal structure of an integral membrane light-harvesting complex from photosynthetic bacteria , 1995, Nature.

[7]  R. Cogdell,et al.  EXCITON LEVEL STRUCTURE AND ENERGY DISORDER OF THE B850 RING OF THE LH2 ANTENNA COMPLEX , 1997 .

[8]  N. Isaacs,et al.  The structure and thermal motion of the B800-850 LH2 complex from Rps.acidophila at 2.0A resolution and 100K: new structural features and functionally relevant motions. , 2003, Journal of molecular biology.

[9]  Klaus Schulten,et al.  Pigment Organization and Transfer of Electronic Excitation in the Photosynthetic Unit of Purple Bacteria , 1997 .

[10]  R. Monshouwer,et al.  Superradiance and Exciton Delocalization in Bacterial Photosynthetic Light-Harvesting Systems , 1997 .

[11]  R. Grondelle,et al.  Energy Transfer in the B800 Rings of the Peripheral Bacterial Light-Harvesting Complexes of Rhodopseudomonas acidophila and Rhodospirillum molischianum Studied with Photon Echo Techniques. , 2000 .

[12]  R. Monshouwer,et al.  Exciton (De)Localization in the LH2 Antenna of Rhodobacter sphaeroides As Revealed by Relative Difference Absorption Measurements of the LH2 Antenna and the B820 Subunit , 1999 .

[13]  R. Silbey,et al.  Current status of single-molecule spectroscopy: Theoretical aspects , 2002 .

[14]  Tomas Gillbro,et al.  Energy Transfer and Exciton Annihilation in the B800−850 Antenna Complex of the Photosynthetic Purple Bacterium Rhodopseudomonas acidophila (Strain 10050). A Femtosecond Transient Absorption Study , 1997 .

[15]  S. Scheuring,et al.  High‐resolution AFM topographs of Rubrivivax gelatinosus light‐harvesting complex LH2 , 2001, The EMBO journal.

[16]  S. Mukamel.  Principles of Nonlinear Optical Spectroscopy , 1995 .

[17]  Tõnu Pullerits,et al.  Photosynthetic light-harvesting: Reconciling dynamics and structure of purple bacterial LH2 reveals function of photosynthetic unit , 1999 .

[18]  R. Cogdell,et al.  Optical and optically detected magnetic resonance investigation on purple photosynthetic bacterial antenna complexes , 1995 .

[19]  Y. Weng,et al.  Determination of the topological shape of integral membrane protein light-harvesting complex LH2 from photosynthetic bacteria in the detergent solution by small-angle X-ray scattering. , 2004, Biophysical journal.

[20]  T. G. Monger,et al.  Triplet states of bacteriochlorophyll and carotenoids in chromatophores of photosynthetic bacteria. , 1976, Biochimica et biophysica acta.

[21]  R. Monshouwer,et al.  Disordered exciton model for the core light-harvesting antenna of Rhodopseudomonas viridis. , 1999, Biophysical journal.

[22]  T. G. Truscott,et al.  Energy transfer between the carotenoid and the bacteriochlorophyll within the B-800-850 light-harvesting pigment-protein complex of Rhodopseudomonas sphaeroides. , 1981, Biochimica et biophysica acta.

[23]  A. V. van Oijen,et al.  Spectroscopy on the B850 band of individual light-harvesting 2 complexes of Rhodopseudomonas acidophila. I. Experiments and Monte Carlo simulations. , 2001, Biophysical journal.

[24]  Jürgen Köhler,et al.  Direct observation of tiers in the energy landscape of a chromoprotein: A single-molecule study , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[25]  William W. Parson,et al.  Light-Harvesting Antennas in Photosynthesis , 2003, Advances in Photosynthesis and Respiration.

[26]  Seogjoo J. Jang,et al.  Single molecule spectroscopy of disordered circular aggregates: A perturbation analysis , 2001 .

[27]  A. Oijen,et al.  Unraveling the electronic structure of individual photosynthetic pigment-protein complexes , 1999, Science.

[28]  V. Sundström,et al.  Energy transfer and trapping in photosynthesis , 1994 .

[29]  N. Isaacs,et al.  Structure‐Based Calculations of the Optical Spectra of the LH2 Bacteriochlorophyll‐Protein Complex from Rhodopseudomonas acidophila , 1996 .

[30]  R. Grondelle.  Excitation energy transfer, trapping and annihilation in photosynthetic systems , 1985 .

[31]  A. V. van Oijen,et al.  Spectroscopy of individual light-harvesting 2 complexes of Rhodopseudomonas acidophila: diagonal disorder, intercomplex heterogeneity, spectral diffusion, and energy transfer in the B800 band. , 2000, Biophysical journal.

[32]  A. V. van Oijen,et al.  Spectroscopy on the B850 band of individual light-harvesting 2 complexes of Rhodopseudomonas acidophila. II. Exciton states of an elliptically deformed ring aggregate. , 2001, Biophysical journal.

[33]  R. G. Alden,et al.  Calculations of Spectroscopic Properties of the LH2 Bacteriochlorophyll−Protein Antenna Complex from Rhodopseudomonas acidophila† , 1997 .

[34]  M. A. Bopp,et al.  The dynamics of structural deformations of immobilized single light-harvesting complexes. , 1999, Proceedings of the National Academy of Sciences of the United States of America.

[35]  R. Grondelle,et al.  Intra- and interband transfers in the B800-B850 antenna of Rhodospirillum molischianum Redfield theory modeling of polarized pump-probe kinetics , 2003 .

[36]  R. Cogdell,et al.  3 – Preparation, Purification, and Crystallization of Purple Bacteria Antenna Complexes , 1993 .