Redox-Bohr effect in the tetrahaem cytochrome c₃ from Desulfovibrio vulgaris: A model for energy transduction mechanisms

Using potentiometric titrations, two protons were found to participate in the redox-Bohr effect observed for cytochrome c₃ from Desulfovibrio vulgaris (Hildenborough). Within the framework of the thermodynamic model previously presented, this finding supports the occurrence of a concerted proton-assisted 2e^- step, ideally suited for the coupling role of cytochrome c₃ to hydrogenase. Furthermore, at physiological pH, it is shown that when sulfate-reducing bacteria use H₂ as energy source, cytochrome c₃ can be used as a charge separation device, achieving energy transduction by energising protons which can be left in the acidic periplasmic side and transferring deenergised electrons to sulfate respiration. This mechanism for energy transduction, using a full thermodynamic data set, is compared to that put forward to explain the proton-pumping function of cytochrome c oxidase.