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 p19-3. 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 60%, 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 OK1-5- and AP19-3. Apparent molecular weights of the three subunits of cytochrome c oxidases were 54,000, 24,000, and 19,000 for strain AP19-3 and 55,000, 24m,000, and 19,000 for strain OK1-50, respect