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  • Title: Mixed-valence cytochrome oxidase-formate complex. A steady-state intermediate.
    Author: Brittain T, Greenwood C, Johnson A.
    Journal: Biochem J; 1977 Dec 01; 167(3):531-4. PubMed ID: 203268.
    Abstract:
    At neutral pH, formate binds to the haem a3 component of cytochrome c oxidase to give a complex that reacts differently from the non-liganded enzyme with reducing agents. Addition of sodium dithionite to the formate complex leads directly to the formation of the fully reduced species, whereas reduction with ascorbate/tetramethylenephenylene-diamine can lead to the production of a mixed-valence species. The stability of this mixed-valence form was studied, and the species appears to represent a 'steady-state' situation that is stable only in the presence of an excess of O2 and reducing equivalents. Characterization of the mixed-valence complex by electron paramagnetic resonance and magnetic circular dichroism reveals the presence of reduced low-spin haem a together with reduced detectable copper and high-spin ferric haem a3.
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