Redox titrations of cytochrome c oxidase. An analysis of a multi-electron system.

Equilibrium redox titrations of cytochrome c oxidase available in the literature are discussed in terms of models with interactions both with respect to oxidation-reduction potentials and the particular property studied. 2. The interaction is restricted to be pairwise. For the present data more complicated forms of interaction are not required. In addition, with this limitation a simple matrix formulation can be used. 3. The EPR titrations require potential interaction involving the hemes and the undetectable Cu. In this way the low intensity of the g6 signal can be accounted for. However, it is shown that there is no unique solution to the problem. 4. The optical titrations at 605 nm can be fitted reasonalby well with the potentials from the EPR data with no spectral interaction. 5. Simulated titrations of magnetic susceptibility show a sensitivity to the model chosen indicating the usefulness of future experiments in this area.