Jul 7, 1999

Oxygen uncouples light absorption by the chlorosome antenna and photosynthetic electron transfer in the green sulfur bacterium chlorobium tepidum

Biochimica Et Biophysica Acta
N Frigaard, K Matsuura


In photosynthetic green sulfur bacteria excitation energy is transferred from large bacteriochlorophyll (BChl) c chlorosome antennas via small BChl a antennas to the reaction centers which then transfer electrons from cytochrome c to low-potential iron-sulfur proteins. Under oxidizing conditions a reversible mechanism is activated in the chlorosomes which quenches excited BChl c. We used flash-induced cytochrome c oxidation to investigate the effect of this quenching on photosynthetic electron transfer in whole cells of Chlorobium tepidum. The extent of cytochrome c photooxidation under aerobic conditions decreased to approx. 3% of that under anaerobic conditions when BChl c was excited under light-limiting conditions. Photooxidation obtained by excitation of BChl a was similar under aerobic and anaerobic conditions. We interpret this drastic decrease in energy transfer from BChl c to the reaction center as a consequence of the quenching mechanism which is activated by O2. This reversible uncoupling of the chlorosome antenna might prevent formation of toxic reactive oxygen species from photosynthetically produced reductants under aerobic conditions. The green filamentous bacterium Chloroflexus aurantiacus also contains chloroso...Continue Reading

  • References12
  • Citations11


  • References12
  • Citations11


Mentioned in this Paper

Energy Transfer
Chloroflexus aurantiacus
Chlorobaculum tepidum
Reaction Center
Iron-Sulfur Proteins

About this Paper

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