Sulfite oxidation catalyzed by aa₃-type cytochrome c oxidase in Acidithiobacillus ferrooxidans

Sulfite is produced as a toxic intermediate during Acidithiobacillus ferrooxidans sulfur oxidation. A. ferrooxidans D3-2, which posseses the highest copper bioleaching activity, is more resistant to sulfite than other A. ferrooxidans strains, including ATCC 23270. When sulfite oxidase was purified homogeneously from strain D3-2, the oxidized and reduced forms of the purified sulfite oxidase absorption spectra corresponded to those of A. ferrooxidans aa₃-type cytochrome c oxidase. The confirmed molecular weights of the α-subunit (52.5 kDa), the β-subunit (25kDa), and the γ-subunit (20 kDa) of the purified sulfite oxidase and the N-terminal amino acid sequences of the γ-subunit of sulfite oxidase (AAKKG) corresponded to those of A. ferrooxidans ATCC 23270 cytochrome c oxidase. The sulfite oxidase activities of the iron-and sulfurgrown A. ferrooxidans D3-2 were much higher than those cytochrome c oxidases purified from A. ferrooxidans strains ATCC 23270, MON-1 and AP19-3. The activities of sulfite oxidase purified from iron-and sulfur-grown strain D3-2 were completely inhibited by an antibody raised against a purified A. ferrooxidans MON-1 aa₃type cytochrome c oxidase. This is the first report to indicate that aa3-type cytochrome c oxidase catalyzed sulfite oxidation in A. ferrooxidans.