THE CYTOCHROME-BD TERMINAL OXIDASE OF AZOTOBACTER-VINELANDII - LOW-TEMPERATURE PHOTODISSOCIATION SPECTROPHOTOMETRY REVEALS REACTIVITY OF CYTOCHROMES-B(595) AND CYTOCHROME-D WITH BOTH CARBON-MONOXIDE AND OXYGEN

Cytochromes d and b(595) were studied by low temperature photodissocia tion 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 Fe-II cytochrome b(595). Oxy-cytochrome d (648 nm) was forme d when the CO adduct was photolysed in the presence of oxygen. This wa s followed by ligand recombination (presumably oxygen) to the high-spi n cytochrome b(595), With a distinctive shift to shorter wavelengths o f the alpha-band of the cytochrome, and a decrease in the oxygenated f orm. All spectral changes were light-reversible. We demonstrate the li ght-reversible binding of CO to both cytochromes b(595) and d, and sug gest migration of oxygen from cytochrome d to cytochrome b595 at a hae m-haem binuclear centre during the oxidase reaction.