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A model is proposed for the active center of cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) in which cytochrome a is a low-spin ferrihemoprotein and cytochrome a3 is a high-spin ferrihemoprotein antiferromagnetically coupled to one of the two Cu2+ ions present in the enzyme. It is further proposed that reduction is accompanied by a conformational change in the enzyme thus exposing the sixth coordination site of cytochrome a3 to ligands. With this model it is possible to account for a variety of outstanding observations including the results of magnetic circular dichroism, Mossbauer, and electron paramagnetic resonance spectroscopies, as well as magnetic susceptibility measurements.
Palmer et al. (Thu,) studied this question.