The B820 sub-unit of the bacterial light-harvesting antenna, a dis-ordered dimer?

Koolhaas, M.H.C.; Mourik, Frank van; Zwan, Gert van der; Grondelle, Rienk van

doi:10.1016/0022-2313(94)90205-4

Cited by 20 publications

(24 citation statements)

References 8 publications

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“…16 Modeling of the influence of the site inhomogeneity on the excitonic spectrum showed that the average dipole strength of the lowest excitonic state of the dimer is about 1.9 times the monomer value. 50 Weighing the exciton spectrum with a Bolzmann distribution using the same method as described above, we find that the average emitting dipole of such a dimer is 1.7 at room temperature with σ/V ) 1, an angle of 20°between the monomers, and V ) 200 cm -1 (not shown). This is somewhat larger than the observed value of 1.3.…”

Section: Discussionmentioning

confidence: 81%

Superradiance and Exciton Delocalization in Bacterial Photosynthetic Light-Harvesting Systems

et al. 1997

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We present temperature-dependent fluorescence quantum yield and lifetime measurements on the LH-1 and LH-2 complexes of Rhodobacter sphaeroides and on the isolated B820 subunit of Rhodospirillum rubrum. From these measurements the superradiance is calculated, which is related to the delocalization of excitations in these complexes. In the B820 preparation we find a radiative rate that is 30% higher than that of monomeric bacteriochlorophyll, in agreement with a dimer model of this subunit. At room temperature both LH-1 and LH-2 are superradiant relative to monomeric Bchl-a with enhancement factors of 3.8 and 2.8, respectively. In LH-2 the radiative rate does not change significantly upon lowering the temperature to 4 K. LH-1 however exhibits a strong temperature dependence, giving rise to a 2.4 times higher radiative rate at 4 K relative to room temperature. From modeling of the superradiance using a Hamiltonian based on the LH-2 structure and including site inhomogeneity, we conclude that the ratio of inhomogeneity over the coupling between the pigments is around 1 for LH-1 and 2-3 for LH-2. From the Monte Carlo simulations we estimate the delocalization length in LH-1 and LH-2 to be on the order of 3-4 pigments at room temperature.

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Section: Discussionmentioning

confidence: 81%

Superradiance and Exciton Delocalization in Bacterial Photosynthetic Light-Harvesting Systems

et al. 1997

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“…This is a complex issue, because the interaction with the surroundings is responsible for this nondegeneracy. In that case additional spectroscopic information (for instance, fluorescence anisotropy of linear dichroism) must be used to unambiguously determine the structure (Koolhaas et al, 1994;Cantor Although we base our analysis on stick spectra, most of the calculated spectra shown are convoluted with a Gaussian line shape, to make them resemble true spectra. This has a marked effect on the positions of the lines, particularly in the case of CD spectra (Somsen et al, 1996).…”

Section: Further Analysis Of the Dimer Structurementioning

confidence: 99%

“…In this paper we only consider stick spectra. The issue of inhomogeneous broadening and the recovery of data from broadened spectra is extremely important for quantitative interpretations (Koolhaas et al, 1994, Somsen, 1995 and will be treated in a subsequent paper (Koolhaas et al, unpublished observations), but will not modify the conclusions drawn here. The organization of this paper is as follows: in the next section we introduce the model we use to calculate the spectra.…”

Section: Introductionmentioning

confidence: 97%

“…The upper and lower exciton components can be identified in the CD and polarized fluorescence excitation spectra and triplet minus singlet measurements Van Mourik et al, 1991), and the excitonic coupling between the pair of BChls is about 230 cm-. From a variety of experiments it became evident that the absorption bandwidth was largely dominated by inhomogeneous broadening (Visschers et al, , 1993De Caro et al, 1994;Pullerits et al, 1995), and a variety of spectral properties of B820 were explained in terms of the "disordered dimer" model Koolhaas et al, 1994). Whether the dimer properties survive upon ring formation is a matter of experimental and theoretical debate.…”

Section: Introductionmentioning

confidence: 99%

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Spectroscopy and structure of bacteriochlorophyll dimers. I. Structural consequences of nonconservative circular dichroism spectra

Koolhaas¹,

Zwan²,

Mourik³

et al. 1997

Biophysical Journal

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The origin of the nonconservative nature of the circular dichroism (CD) spectrum of bacteriochlorophyll dimers is investigated. It is shown that coupling between the Qy and Qx transitions can, under rather restricting circumstances, lead to an asymmetrical CD spectrum: only for a limited set of relative orientations of the monomers within the dimer is the spectrum found to be asymmetrical. The relation between intensity and asymmetry of the CD spectrum is elucidated. The results are applied to the B820 subunit of the LH1 antenna system and subsequently to the antenna system LH1 itself. Differences in the geometry of the BChls in LH1 versus the LH2 structure are discussed.

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“…Inclusion of inhomogeneous broadening into the exciton calculations, for instance introduced by assuming that the site energies are taken randomly from an IDF, has effect on both the relative magnitude and the polarisation of the exciton bands [28,39,401. A remarkable effect is that "forbidden" exciton bands may become partially "allowed" in the presence of disorder.…”

Section: Structure and Spectroscopy Of Lh1/2mentioning

confidence: 99%

Photosynthetic antennae. Photosynthetic light‐harvesting

Grondelle

Monshouwer

Valkūnas

1996

Ber Bunsenges Phys Chem

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The peripheral light-harvesting complex of the photosynthetic bacterium Rhodopseudomonas acidophila (LH2) and the major plant light-harvesting complex LHCII have a very similar function: to absorb solar photons and to transfer the electronic excitation to the pigments surrounding the reaction center, the so-called 'core'. Nevertheless, their structures exhibit a dramatically different arrangement of the pigments. In LH2 the bacteriochlorophyll molecules are arranged in a highly symmetric ring, while in LHCII the positioning of the chlorophylls is very irregular. In both complexes the average distance between the pigments is 1 nm or less and, as a consequence, the electronic interaction between the pigments is strong (> 100 cm-I). Therefore, the excitation transport in these photosynthetic light-harvesting systems can not be described by a simple Fdrster type transfer mechanism, but new or other transfer mechanisms may be operative, for instance a mechanism in which the excitation is to some extent delocalized. Crucial parameters are the strength of the electronic coupling, the amount of energetic disorder and/or heterogeneity and the nature and strength of the interactions of the pigments with the protein. Here we will discuss the current status of the field of photosynthetic energy transfer in particular for LH2. We will evaluate a few simple models that contain some of the essential ingredients to describe the process of energy transfer and finally we will discuss some of the perspectives in this scientific field.

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The B820 sub-unit of the bacterial light-harvesting antenna, a dis-ordered dimer?

Cited by 20 publications

References 8 publications

Superradiance and Exciton Delocalization in Bacterial Photosynthetic Light-Harvesting Systems

Superradiance and Exciton Delocalization in Bacterial Photosynthetic Light-Harvesting Systems

Spectroscopy and structure of bacteriochlorophyll dimers. I. Structural consequences of nonconservative circular dichroism spectra

Photosynthetic antennae. Photosynthetic light‐harvesting

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