The cytochrome bo quinol oxidase of Escherichia coli is homologous in sequence and in structure to cytochrome aa 3 type cytochrome oxidase in subunit 1, which contains the catalytic core. The cytochrome bo enzyme forms a formate complex which exhibits ‘g = 12’ and ‘g = 2.9’ EPR signals at X band; similar signals have previously been observed only in association with the ‘slow’ and formate-ligated states of cytochrome oxidase. These signals arise from transitions within integral spin multiplets identified with the homologous heme-copper binuclear catalytic centers in both enzymes.
