Purification and some properties of sulfur:ferric ion oxidoreductase from Thiobacillus ferrooxidans.
A sulfur:ferric ion oxidoreductase that utilizes ferric ion (Fe3+) as an electron acceptor of elemental sulfur was purified from iron-grown Thiobacillus ferrooxidans to an electrophoretically homogeneous state. Under anaerobic conditions in the presence of Fe3+, the enzyme reduced 4 mol of Fe3+ with 1 mol of elemental sulfur to give 4 mol of Fe2+ and 1 mol of sulfite, indicating that it corresponds to a ferric ion-reducing system (T. Sugio, C. Domatsu, O. Munakata, T. Tano, and K. Imai, Appl. Environ. Microbiol. 49:1401-1406, 1985). Under aerobic conditions, sulfite, but not Fe2+, was produced during the oxidation of elemental sulfur by this enzyme because the Fe2+ produced was rapidly reoxidized chemically by molecular oxygen. The possibility that Fe3+ serves as an electron acceptor under aerobic conditions was ascertained by adding o-phenanthroline, which chelates Fe2+, to the reaction mixture. Sulfur:ferric ion oxidoreductase had an apparent molecular weight of 46,000, and it is composed of two identical subunits (Mr = 23,000) as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Sulfur oxidation by this enzyme was absolutely dependent on the presence of reduced glutathione. The enzyme had an isoelectric point and a pH optimum at pH 4.6 and 6.5, respectively. Almost all the activity of sulfur:ferric ion oxidoreductase was observed in the osmotic shock fluid of the cells, suggesting that it was localized in the periplasmic space of the cells.
Sugio
T
T
Division of Biological Function and Genetic Resources Science, Faculty of Agriculture, Okayama University, Japan.
Mizunashi
W
W
Inagaki
K
K
Tano
T
T
D005978:Glutathione / Q000494:pharmacology; D007700:Kinetics; D008970:Molecular Weight; D010088:Oxidoreductases / Q000302:isolation & purification* / Q000378:metabolism; D013855:Thiobacillus / Q000201:enzymology*
D010088:Oxidoreductases; C053995:sulfur-ferric ion oxidoreductase; D005978:Glutathione