The Determination of the Electrochemical Potential Difference of Protons in Bacterial Chromatophores

  • Rita Casadio
  • Giovanni Venturoli
  • B. Andrea Melandri
Part of the NATO ASI Series book series (NSSA, volume 91)


In cells and in subcellular vesicles, a thermodynamic description of the energy-driven metabolic reactions is based on the evaluation of the free energy change which results from the vectorial proton movements across the coupling membrane. According to the chemiosmotic hypothesis for energy coupling introduced by P.Mitchell(1), the bulk to bulk phase electrochemical potential difference of protons (\(\Delta {{\tilde{\mu }}_{{{H}^{+}}}} \)) is the driving force for ATP synthesis and active transport in all energy conserving membranes. In the last decade, many experiments were performed in order to test the validity of the chemiosmotic hypothesis in energy conserving systems such as bacteria, mitochondria, chloroplast and bacterial chromatophores. A common feature of these studies was to determine the extent of \(\Delta {{\tilde{\mu }}_{{{H}^{+}}}} \) sustained by substrate oxidation or light-driven electron flow, and to compare it to thermodynamic and kinetic parameters of the phosphorylation reaction and of metabolite transport across the coupling membrane. Many efforts were, therefore, done in order to find and develop methods and techniques suited to monitor \(\Delta {{\tilde{\mu }}_{{{H}^{+}}}} \) especially in those vesicular systems, where a direct evaluation was prevented by the smallness of the internal lumen.


Flow Dialysis Reaction Center Complex Outer Compartment Coupling Membrane Single Turnover Flash 
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Copyright information

© Plenum Press, New York 1985

Authors and Affiliations

  • Rita Casadio
    • 1
  • Giovanni Venturoli
    • 1
  • B. Andrea Melandri
    • 1
  1. 1.Institute of BotanyUniversity of BolognaBolognaItaly

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