Isolation and Some Properties of Cytochrome c Oxidase Purified from a Bisulfite Ion Resistant Thiobacillus ferrooxidans Strain, OK1-50

Sulfite ion (HSO₃⁻) is one of the products when elemental sulfur is oxidized by the hydrogen sulfide:ferric ion oxidoreductase of Thiobacillus ferrooxidans AP19-3. Under the conditions in which HSO₃⁻ is accumulated in the cells, the iron oxidase of this bacterium was strongly inhibited by HSO₃⁻. Since cytochrome c oxidase is one of the most important components of the iron oxidase enzyme system in T. ferrooxidans, effects of HSO₃⁻ on cytochrome c oxidase activity were studied with the plasma membranes of HSO₃⁻-resistant and -sensitive strains of T. ferrooxidans, OK1-50 and AP19-3. The enzyme activity of AP19-3 compared with OK1-50 was strongly inhibited by HSO₃⁻. To investigate the inhibition mechanism of HSO₃⁻ in T. ferrooxidans, cytochrome c oxidases were purified from both strains to an electrophoretically homogeneous state. Cytochrome c oxidase activity of a purified OK1-50 enzyme was not inhibited by 5 mM HSO₃⁻. In contrast, the same concentration of HSO₃⁻ inhibited the enzyme activity of AP19-3 50%, indicating that the cytochrome c oxidase of OK1-50 was more resistant to HSO₃⁻ than that of AP19-3. Cytochrome c oxidases purified from both strains were composed of three subunits. However, the molecular weight of the largest subunit differed between OK1-50 and AP19-3. Apparent molecular weights of the three subunits of cytochrome c oxidases were 53,000, 24,000, and 19,000 for strain AP19-3 and 55,000, 24,000, and 19,000 for strain OK1-50, respectively.