Excitation dynamics in strongly bounded associates of B800–850 and B800–830 complexes from photosynthetic purple bacterium Thiorhodospira sibirica

Biochemistry (Moscow) Supplement Series A Membrane and Cell Biology 01/2007; 1(4):336-342. DOI: 10.1134/S1990747807040101

ABSTRACT Strongly bounded associates of B800–850 (LH2) and B800–830 (LH3) complexes from photosynthetic purple bacterium Thiorhodospira sibirica were investigated. It was shown that associates contain 8–10 complexes (LH2:LH3 ≈ 1:1). Absorption spectra of the monomer
LH2 and the monomer LH3 complexes were calculated. Excitation of B800 absorption band of associates results in: (i) intracomplex
excitation energy transfer from B800 to B830 or B850 with time constant of about 500 fs; (ii) intercomplex excitation energy
transfer from B820 band of LH3 complex to B850 band of LH2 complex with time constant of about 2.5 ps; (iii) excitation deactivation
in B850 band of LH2 complex with time constant of about 800 ps. Signal polarization at long-wavelength side of associates
absorption spectrum near 900 nm was negative (−0.1). The interaction of LH3 and LH2 complexes in associates is, to some extent,
analogous to the interaction of LH2 and LH1 complexes in chromatophores. Time constant of excitation energy transfer between
LH3 and LH2 complexes in associates may be regarded as a minimal time constant for energy transfer between the peripheral
and core antenna complexes.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The light-harvesting complex I (LH-I) of Rhodobacter sphaeroides has been modeled computationally as a hexadecamer of alphabeta-heterodimers, based on a close homology of the heterodimer to that of light-harvesting complex II (LH-II) of Rhodospirillum molischianum. The resulting LH-I structure yields an electron density projection map that is in agreement with an 8.5-A resolution electron microscopic projection map for the highly homologous LH-I of Rs. rubrum. A complex of the modeled LH-I with the photosynthetic reaction center of the same species has been obtained by a constrained conformational search. This complex and the available structures of LH-II from Rs. molischianum and Rhodopseudomonas acidophila furnish a complete model of the pigment organization in the photosynthetic membrane of purple bacteria.
    Biophysical Journal 09/1998; 75(2):683-94. · 3.83 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Two color transient absorption measurements were performed on a LH2 complex from Rhodospirillum molischianum by using several excitation wavelengths (790, 800, 810, and 830 nm) and probing in the spectral region from 790 to 870 nm at room temperature. The observed energy transfer time of 1.0 ps from B800 to B850 at room temperature is longer than the corresponding rates in Rhodopseudomonas acidophila and Rhodobacter sphaeroides. We observed variations (0.9−1.2 ps) of B800−850 energy transfer times at different B800 excitation wavelengths, the fastest time (0.9 ps) was obtained with 800 nm excitation. At 830 nm excitation the energy transfer to the B850 ring takes place within 0.5 ps. The measured kinetics, as well as steady-state absorption and CD spectra, are consistent with those calculated with the configuration interaction exciton method (CIEM) [Linnanto et al. J. Phys. Chem. B 1999, 103, 8739]. Fully excitonic simulation of the CD spectrum of the LH2 of Rs. molischianum is presented for the first time. The calculations put the E3 exciton states of B850 near the narrow excitonic B800 manifold and according to our model, these states provide the main route of energy transfer from the B800 ring to the B850 ring in the complex. The 1,2E2 states at 824 nm predicted by the calculations serve as an additional energy transfer channel as indicated by the observed fast transfer rate at 830 nm excitation.
    The Journal of Physical Chemistry B 09/2001; 105:9849. · 3.38 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Femtosecond one-color pump−probe measurements were performed on the B800−820 light-harvesting antenna complex of Rhodopseudomonas acidophila, strain 7750, at room and low temperature (mainly 77 K). The isotropic and anisotropic decays obtained within the B800 band are clearly wavelength- and temperature-dependent. A fast isotropic decay component at room temperature was found to have a lifetime of 0.30 ps at 784 nm, 0.54 ps at 790 nm, and 0.75 ps at 800 nm. The interband energy-transfer time was found to be 0.75 ps at room temperature, which slows down to 0.90 ps at 77 K. The time-resolved anisotropy, obtained around 790 and 800 nm, exhibits a single-exponential decay feature with a depolarization time of 1.1 ps at room temperature and 450 fs at 77 K. Measurements within the B820 band showed a fast isotropic component having a lifetime 60−80 fs. The corresponding time-resolved anisotropy decay occurs in 100−130 fs at room temperature and 240 fs at 77 K. In view of the general similarity in the energy-transfer dynamics between the B800−820 complex and other LH2 antenna, we conclude that the markedly blue-shifted B820 band has no substantial effect on the interband transfer rate.
    Journal of Physical Chemistry B - J PHYS CHEM B. 01/1998; 102(5).