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Anoxygenic photosynthesis is a phototrophic process that captures light energy to drive carbon fixation without producing molecular oxygen. Unlike oxygenic photosynthesis, which utilizes water as an electron donor and releases oxygen, anoxygenic phototrophs use alternative electron donors such as hydrogen sulfide (H₂S), elemental sulfur (S⁰), or thiosulfate (S₂O₃²⁻). This process is carried out by diverse groups of bacteria, including purple bacteria, green...
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Updated: May 5, 2026

Electrochemical Detection of Deuterium Kinetic Isotope Effect on Extracellular Electron Transport in Shewanella oneidensis MR-1
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Sulfide-quinone and sulfide-cytochrome reduction in Rhodobacter capsulatus.

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Sulfide reduction of ubiquinone in Rhodobacter capsulatus involves the cytochrome bc1 complex, similar to sulfide-quinone reductase found in other organisms. This suggests a conserved electron transport pathway for sulfide oxidation.

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Area of Science:

  • Microbiology
  • Biochemistry
  • Photosynthesis

Background:

  • Sulfide oxidation is a key process in microbial metabolism.
  • Ubiquinone and cytochromes are crucial electron carriers in biological systems.
  • Rhodobacter capsulatus is a model organism for studying photosynthesis and electron transport.

Purpose of the Study:

  • To investigate the mechanism of sulfide reduction of ubiquinone in Rhodobacter capsulatus.
  • To compare this process with cytochrome reduction.
  • To elucidate the role of the ubiquinone pool and cytochrome bc1 complex in sulfide oxidation.

Main Methods:

  • Enzymatic assays using isolated chromatophores.
  • Kinetic analysis of electron transport rates (Vmax and Km).
  • Inhibition studies using KCN and other specific inhibitors.

Main Results:

  • Sulfide-dependent ubiquinone reduction exhibited a Vmax of 300 μmoles/mg bacteriochlorophyll a·h and Km of 5 μM.
  • Cytochrome c reduction showed a Vmax of 10 μmoles/mg bacteriochlorophyll a·h and Km of 3 μM.
  • Both reactions were sensitive to KCN, indicating involvement of sulfide-quinone reductase (SQR).

Conclusions:

  • Sulfide oxidation in Rhodobacter capsulatus utilizes the ubiquinone pool.
  • The cytochrome bc1 complex is likely involved in electron transfer from sulfide.
  • The findings suggest a conserved mechanism for sulfide oxidation across different organisms.