Contains siroheme, [4Fe-4S] cluster, FAD and FMN. The enzyme, which catalyses the six-electron reduction of sulfite to sulfide, is involved in sulfate assimilation in bacteria and yeast. Different from EC
1.8.1.22, dissimilatory sulfite reductase system, which is involved in prokaryotic sulfur-based energy metabolism. cf. EC
1.8.7.1, assimilatory sulfite reductase (ferredoxin).