title: Mixed-valence cytochrome oxidase-formate complex. A steady-state intermediate.
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.
mesh_terms: D001205:Ascorbic Acid; D002942:Circular Dichroism; D004578:Electron Spin Resonance Spectroscopy; D003576:Electron Transport Complex IV / Q000378:metabolism*; D005561:Formates / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen; D013772:Tetramethylphenylenediamine
chemical_list: D005561:Formates; D003576:Electron Transport Complex IV; D013772:Tetramethylphenylenediamine; D001205:Ascorbic Acid; D010100:Oxygen