title: Siroheme as an active catalyst in sulfite reduction.
abstract: Siroheme extracted by acetone/HCl treatment of sulfite reductase from yeast and purified by column chromatography catalyzed the reduction of sulfite to thiosulfate and sulfide when coupled with a hydrogen-hydrogenase-methyl viologen system. The activity increased with decrease in pH from 7 to 4, and an apparent Km value of 50 mM for sulfite was obtained. In contrast to sirohydrochlorin plus Fe2+, addition of inorganic iron or 2,2'-bipyridine prior to the reduction reaction had scarcely any effect on the sulfite-reducing activity of siroheme. Hydroxylamine was reduced by siroheme at a much faster rate than sulfite, and the rate increased with increase in pH from 6 to 9. Siroheme extracted from Chromatium vinosum strain D sulfite reductase also reduced sulfite to thiosulfate and sulfide.
mesh_terms: D002384:Catalysis; D055598:Chemical Phenomena; D002621:Chemistry; D006418:Heme / Q000031:analogs & derivatives*; D006863:Hydrogen-Ion Concentration; D019811:Hydroxylamine; D006898:Hydroxylamines; D010088:Oxidoreductases; D050862:Oxidoreductases Acting on Sulfur Group Donors; D013447:Sulfites
chemical_list: D006898:Hydroxylamines; D013447:Sulfites; D019811:Hydroxylamine; D006418:Heme; C009272:siroheme; D010088:Oxidoreductases; D050862:Oxidoreductases Acting on Sulfur Group Donors