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

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.