Abstract
The significance of potentiometric titrations carried out in situ, i.e. within the biological membrane, is discussed with respect to the pH dependence of formal potentials. Results obtained using this method on membrane-bound proteins constituting the bc complex of photosynthetic bacteria are reconsidered. The discussion is based on the theoretical treatment of a recent electrochemical investigation into cytochrome c carried out by Ikeshoji and coworkers in 1989. These authors drew attention to differences between equilibrium reaction and conformational transition coupled protonations. Reasons are given as to why in-situ titrations are not able to differentiate these. The relevance of this to current working hypotheses of the bc complex are considered. A novel working hypothesis for proton transport by this complex is presented, including both equilibrium and conformation coupled protonations. Reaction kinetic calculations supporting this hypothesis are performed.
Published Version
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