LZ, Tano T: Purification and some properties of sulfite:ferric ion oxidoreductase from Thiobacillus ferrooxidans

Sulfite:ferric ion oxidoreductase in the plasma membrane of Thiobaciusferrooxidans AP19-3 was purified to an electrophoretically homogeneous state. The enzyme had an apparent molecular weight of 650,000 and was composed of two subunits (M1s, 61,000 and 59,000) as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The Michaelis constants of sulfite:ferric ion oxidoreductase for Fe3 ' and sulfite ions were 1.0 and 0.071 mM, respectively. Sulfite:ferric ion oxidoreductase suffered from end product inhibition by 1 mM Fe2+. The iron-oxidizing bacterium Thiobacillus ferrooxidans inhabits acid mine drainage containing a large amount of ferrous and ferric ions. A unique enzyme, hydrogen sulfide: ferric ion oxidoreductase (SFORase), which uses ferric ion as an electron acceptor for oxidation of sulfide, was recently purified to an electrophoretically homogeneous state (15, 18, 20) from iron-grown T. ferrooxidans AP19-3. Originally, SFORase was thought to oxidize elemental sulfur directly, but now it is thought to actually use sulfide (18). SFORas