ISOLATION AND SOME PROPERTIES OF CYTOCHROME-C-OXIDASE PURIFIED FROM ABISULFITE ION RESISTANT THIOBACILLUS-FERROOXIDANS STRAIN, OK1-50

Sulfite ion (HSO3-) is one of the products when elemental sulfur is ox idized by the hydrogen sulfide:ferric ion oxidoreductase of Thiobacill us ferrooxidans AP19-3. Under the conditions in which HSO3- is accumul ated in the cells, the iron oxidase of this bacterium was strongly inh ibited by HSO3-. Since cytochrome c oxidase is one of the most importa nt components of the iron oxidase enzyme system in T. ferrooxidans, ef fects of HSO3- on cytochrome c oxidase activity were studied with the plasma membranes of HSO3--resistant and -sensitive strains of T. ferro oxidans, OK1-50 and AP19-3. The enzyme activity of AP19-3 compared wit h OK1-50 was strongly inhibited by HSO3-. To investigate the inhibitio n mechanism of HSO3- in T. ferrooxidans, cytochrome c oxidases were pu rified from both strains to an electrophoretically homogeneous state. Cytochrome c oxidase activity of a purified OK1-50 enzyme was not inhi bited by 5 mM HSO3-. In contrast, the same concentration of HSO3- inhi bited the enzyme activity of AP19-3 50%, indicating that the cytochrom e 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 thr ee subunits. However, the molecular weight of the largest subunit diff ered between OK1-50 and AP19-3. Apparent molecular weights of the thre e subunits of cytochrome c oxidases were 53,000, 24,000, and 19,000 fo r strain AP19-3 and 55,000, 24,000, and 19,000 for strain OK1-50, resp ectively.