The cytochromebdterminal oxidase ofAzotobacter vinelandii: Low temperature photodissociation spectrophotometry reveals reactivity of cytochromesb595anddwith both carbon monoxide and oxygen

Cytochromes d and b595 were studied by low temperature photodissociation of CO-ligated Azotobacter vinelandii membranes. White light or He-Ne laser irradiation revealed 436 and 594–597 nm absorption bands to be due to Fe11 cytochrome b595. Oxy-cytochrome d (648 nm) was formed when the CO adduct was photolysed in the presence of oxygen. This was followed by ligand recombination (presumably oxygen) to the high-spin cytochrome b595, with a distinctive shift to shorter wavelengths of the α-band of the cytochrome, and a decrease in the oxygenated form. All spectral changes were light-reversible. We demonstrate the light-reversible binding of CO to both cytochromes b595 and d, and suggest migration of oxygen from cytochrome d to cytochrome b595 at a haem-haem binuclear centre during the oxidase reaction.