Photosynthesis Research

, Volume 71, Issue 1–2, pp 99–123 | Cite as

The quantitative relationship between structure and polarized spectroscopy in the FMO complex of Prosthecochloris aestuarii: refining experiments and simulations

  • Markus Wendling
  • Milosz A. Przyjalgowski
  • Demet Gülen
  • Simone I. E. Vulto
  • Thijs J. Aartsma
  • Rienk van Grondelle
  • Herbert van Amerongen


New absorption, linear dichroism (LD) and circular dichroism (CD) measurements at low temperatures on the Fenna—Matthews—Olson complex from Prosthecochloris aestuarii are presented. Furthermore, the anisotropy of fluorescence excitation spectra is measured and used to determine absolute LD spectra, i.e. corrected for the degree of orientation of the sample. In contrast to previous studies, this allows comparison of not only the shape but also the amplitude of the measured spectra with that calculated by means of an exciton model. In the exciton model, the point-dipole approximation is used and the calculations are based on the trimeric structure of the complex. An improved description of the absorption and LD spectra by means of the exciton model is obtained by simply using the same site energies and coupling strengths that were given by Louwe et al. (1997, J Phys Chem B 101: 11280–11287) and including three broadening mechanisms, which proved to be essential: Inhomogeneous broadening in a Monte Carlo approach, homogeneous broadening by using the homogeneous line shape determined by fluorescence line-narrowing measurements [Wendling et al. (2000) J Phys Chem B 104: 5825–5831] and lifetime broadening. An even better description is obtained when the parameters are optimized by a global fit of the absorption, LD and CD spectra. New site energies and coupling strengths are estimated. The amplitude of the LD spectrum is described quite well. The shape of the CD spectrum is modelled in a satisfactory way but its size can only be simulated by using a rather large value for the index of refraction of the medium surrounding the chromophores. It is shown that the estimated coupling strengths are compatible with the value of the dipole strength of bacteriochlorophyll a, when using the empty-cavity model for the local-field correction factor.

circular dichroism electron-phonon coupling excitons homogeneous line shape inhomogeneous broadening lifetime broadening light harvesting linear dichroism modeling photosynthesis pigment–protein complex polarized fluorescence polarized spectroscopy 


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Copyright information

© Kluwer Academic Publishers 2002

Authors and Affiliations

  • Markus Wendling
    • 1
  • Milosz A. Przyjalgowski
    • 1
  • Demet Gülen
    • 2
  • Simone I. E. Vulto
    • 3
  • Thijs J. Aartsma
    • 3
  • Rienk van Grondelle
    • 1
  • Herbert van Amerongen
    • 1
  1. 1.Division of Physics and Astronomy, Department of Biophysics and Physics of Complex SystemsVrije Universiteit, Faculty of SciencesAmsterdamThe Netherlands
  2. 2.Department of PhysicsMiddle East Technical UniversityAnkaraTurkey
  3. 3.Department of Biophysics, Huygens LaboratoryRijksuniversiteit LeidenLeidenThe Netherlands

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