THE FERROUS-OXY INTERMEDIATE IN THE REACTION OF DIOXYGEN WITH FULLY REDUCED CYTOCHROMES AA(3) AND BO(3)

We have studied the reactions with oxygen of two terminal oxidases, cy tochrome c oxidase from mitochondria and cytochrome bo(3) from Escheri chia coli. In each case, flow-flash methodology was used to react the fully reduced enzyme with a high concentration of oxygen (1 mM), and a bsorbance changes were recorded for a number of separate wavelengths i n the alpha-band (visible) region. In both enzymes, an early kinetic p hase could be resolved, corresponding to the binding of oxygen to prod uce a ferrous-oxy heme intermediate. In cytochrome c oxidase, this int ermediate appears with a time constant of 10 mu s; its spectrum has a peak at 595 nm (relative to the unliganded reduced enzyme). In cytochr ome bo(3), the ferrous-oxy intermediate, resolved by optical absorbanc e spectroscopy for the first time, appears with a time constant of 11 mu s and has a broad maximum near 570 nm.