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Optical and structural properties of chlorosomes of the photosynthetic green sulfur bacteriumChlorobium limicola

Authors
Journal
Biochimica et Biophysica Acta (BBA) - Bioenergetics
0005-2728
Publisher
Elsevier
Publication Date
Volume
848
Issue
1
Identifiers
DOI: 10.1016/0005-2728(86)90162-3
Keywords
  • Bacteriochlorophylla
  • Bacteriochlorophyllc
  • Energy Transfer
  • Chlorosome
  • (Green Sulfur Bacterium)
Disciplines
  • Biology
  • Physics

Abstract

Abstract Isolated chlorosomes of the photosynthetic green sulfur bacterium Chorobium limicola upon cooling to 4 K showed, in addition to the near-infrared absorption band at 753 nm due to bacteriochlorophyll c, a weak band near 800 nm that could be attributed to bacteriochlorophyll a. The emission spectrum showed bands of bacteriochlorophyll c and a at 788 and 828 nm, respectively. The fluorescence excitation spectrum indicated a high efficiency of energy transfer from bacteriochlorophyll c to bacteriochlorophyll a. When all bacteriochlorophyll c absorption had been lost upon storage, no appreciable change in the optical properties of the bacteriochlorophyll a contained in these ‘depleted chlorosomes’ was observed. The fluorescence and absorption spectra of the chlorosomal bacteriochlorophyll a were clearly different from those of the soluble bacteriochlorophyll a protein present in these bacteria. The results provide strong evidence that bacteriochlorophyll a, although present in a small amount, is an integral constituent of the chlorosome. It presumably functions in the transfer of energy from the chlorosome to the photosynthetic membrane; its spectral properties and the orientation of its near-infrared optical transitions as determined by linear dichroism are such as to favor this energy transfer.

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