The dinuclear center of cytochrome bo3 from Escherichia coli

For the study of the dinuclear center of heme-copper oxidases cytochrome bo(3) from Escherichia coli offers several advantages over the extensively characterized bovine cytochrome c oxidase. The availability of strains with enhanced levels of expression allows purification of the signifi cant amounts of enzyme required for detailed spectroscopic studies. Cytochrome bo(3) is readily prepared as the fast form, with a homogeneous dinuclear center which gives rise to characteristic broad EPR signals not seen in CcO. The absence of Cu-A and the incorporation of protohemes allows for a detailed interpretation of the MCD spectra arising from the dinuclear center heme o(3). Careful analysis allows us to distinguish between small molecules that bind to heme o(3), those which are ligands of Cu-B, and those which react to yield higher oxidation states of heme o(3). Here we review results from our studies of the reactions of fast cytochrome bo(3) with formate, fluoride, chloride, azide, cyanide, NO, and H2O2.