Photosynthesis Research

, Volume 100, Issue 2, pp 67–78

Anisotropic distribution of emitting transition dipoles in chlorosome from Chlorobium tepidum: fluorescence polarization anisotropy study of single chlorosomes

  • Yutaka Shibata
  • Yoshitaka Saga
  • Hitoshi Tamiaki
  • Shigeru Itoh
Regular Paper

DOI: 10.1007/s11120-009-9429-z

Cite this article as:
Shibata, Y., Saga, Y., Tamiaki, H. et al. Photosynth Res (2009) 100: 67. doi:10.1007/s11120-009-9429-z

Abstract

The polarization anisotropy of fluorescence spectra from single chlorosomes isolated from a green sulfur bacterium, Chlorobium (Cb.) tepidum, was observed at 13 K. As the polarizer was rotated, the intensities of the fluorescence bands of both bacteriochlorophyll (BChl)-c self-aggregates and BChl-a in baseplate proteins showed clear oscillations. From the oscillation, the values of the degree of polarization (DP) and the phase shift (PS) between the BChl-c and BChl-a bands were determined for each single chlorosome. The DP versus PS plot for Cb. tepidum chlorosomes showed linear correlations between the PS and the DP values for both BChl-c and BChl-a fluorescence bands. This tendency could be explained from a simulation assuming a random orientation of chlorosomes and a triaxial orientation distribution of emitting transition dipoles within a single chlorosome. The intensity ratios among the X-/Y-/Z-principal transition dipoles were estimated to be 0.3/0.5/1 and 1/0.6/0.1 for the BChl-c and BChl-a fluorescence bands, respectively. Here, the X-, Y-, and Z-axes are perpendicular, parallel to the cytoplasmic membrane, and parallel to the chlorosome long axis, respectively. A theoretical calculation based on the exciton theory was conducted to reproduce the observed triaxial orientation distribution of emitting transition dipoles. The simulation revealed that a deformation introduced to the circular cross section of the rod-shaped BChl-c self-aggregates could qualitatively reproduce results of this study.

Keywords

Fluorescence polarization anisotropy Confocal microscope Single molecule spectroscopy Photosynthetic antenna complex Bacteriochlorophyll-c Green photosynthetic bacteria 

Abbreviations

BChl

Bacteriochlorophyll

Cb

Chlorobium

Cfl

Chloroflexus

DP

Degree of polarization

PS

Phase shift

FMO

Fenna-Matthews-Olson

EM

Electron microscope

LD

Linear dichroism

CD

Circular dichroism

CCD

Charge-coupled device

FWHM

Full width at half maximum

NMR

Nuclear magnetic resonance

Copyright information

© Springer Science+Business Media B.V. 2009

Authors and Affiliations

  • Yutaka Shibata
    • 1
  • Yoshitaka Saga
    • 2
  • Hitoshi Tamiaki
    • 3
  • Shigeru Itoh
    • 1
  1. 1.Department of Physics, Graduate School of ScienceNagoya UniversityNagoyaJapan
  2. 2.Department of Chemistry, Faculty of Science and EngineeringKinki UniversityHigashi-OsakaJapan
  3. 3.Department of Bioscience and Biotechnology, Faculty of Science and EngineeringRitsumeikan UniversityKusatsuJapan