A model for cytochrome oxidase.

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Abstract
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 1 of the 2 Cu2+ ions present in the enzyme. Reduction may then be accompanied by a conformational change in the enzyme thus exposing the 6th coordination site of cytochrome a3 to ligands. This model accounts for a variety of observations including the results of magnetic circular dichroism, Mossbauer and EPR spectroscopies, as well as magnetic susceptibility measurements.