The enzyme is essential in prokaryotic sulfur-based energy metabolism, including sulfate/sulfite reducing organisms, sulfur-oxidizing bacteria, and organosulfonate reducers. In sulfur reducers it catalyses the reduction of sulfite to sulfide (reaction 1), while in sulfur oxidizers it catalyses the opposite reaction (reaction 2).[2] The reaction involves the small protein DsrC, which is present in all the organisms that contain dissimilatory sulfite reductase.[3] During the process an intramolecular trisulfide is formed between two L-cysteine residues of DsrC and the sulfur atom from sulfite.[4] This trisulfide can be reduced by a number of proteins including DsrK and TcmB.[5]
Reaction in organisms performing dissimilatory sulfate reduction:
(2a) a [DsrC protein]-S-sulfanyl-L-cysteine + 3 acceptor + 3 H2O = a [DsrC]-S-sulfo-L-cysteine + 3 reduced acceptor + H+
(2b) a [DsrC]-S-sulfo-L-cysteine = sulfite + a [DsrC protein]-disulfide
The systematic name of this enzyme class is hydrogen-sulfide:[DsrC sulfur-carrier protein],acceptor oxidoreductase.
This enzyme is different from EC 1.8.1.2, assimilatory sulfite reductase (NADPH), and EC 1.8.7.1, assimilatory sulfite reductase (ferredoxin), which are involved in sulfate assimilation.
^Parey K, Warkentin E, Kroneck PM, Ermler U (October 2010). "Reaction cycle of the dissimilatory sulfite reductase from Archaeoglobus fulgidus". Biochemistry. 49 (41): 8912–21. doi:10.1021/bi100781f. PMID20822098.
^Schedel M, Vanselow M, Trüper HG (1979). "Siroheme sulfite reductase isolated from Chromatium vinosum. Purification and investigation of some of its molecular and catalytic properties". Archives of Microbiology. 121 (1): 29–36. Bibcode:1979ArMic.121...29S. doi:10.1007/BF00409202. S2CID22126920.