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Dissimilatory sulfite reductase (EC 1.8.99.5) is an enzyme that participates in sulfur metabolism in dissimilatory sulfate reduction.

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). The reaction involves the small protein DsrC, which is present in all the organisms that contain dissimilatory sulfite reductase. During the process an intramolecular trisulfide is formed between two L-cysteine residues of DsrC and the sulfur atom from sulfite. This trisulfide can be reduced by a number of proteins including DsrK and TcmB.

Reaction in organisms performing dissimilatory sulfate reduction:

(1) sulfite + a -dithiol + 2 reduced acceptor + 2 H = hydrogen sulfide + a -disulfide + 2 acceptor + 3 H₂O (overall reaction)

(1a) sulfite + a -dithiol + 2 reduced acceptor + 2 H = a -S-sulfanyl-L-cysteine + 2 acceptor + 3 H₂O

(1b) a -S-sulfanyl-L-cysteine = hydrogen sulfide + a -disulfide

Reaction in organisms performing sulfur oxidation:

(2) a -S-sulfanyl-L-cysteine + 3 acceptor + 3 H₂O = sulfite + a -disulfide + 3 reduced acceptor + 2 H (overall reaction)

(2a) a -S-sulfanyl-L-cysteine + 3 acceptor + 3 H2O = a -S-sulfo-L-cysteine + 3 reduced acceptor + H

(2b) a -S-sulfo-L-cysteine = sulfite + a -disulfide

The systematic name of this enzyme class is hydrogen-sulfide:,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.

References

1. 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. PMID 20822098.
2. 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. S2CID 22126920.
3. Oliveira TF, Vonrhein C, Matias PM, Venceslau SS, Pereira IA, Archer M (December 2008). "The crystal structure of Desulfovibrio vulgaris dissimilatory sulfite reductase bound to DsrC provides novel insights into the mechanism of sulfate respiration". The Journal of Biological Chemistry. 283 (49): 34141–9. doi:10.1074/jbc.M805643200. PMC 2662231. PMID 18829451.
4. Santos AA, Venceslau SS, Grein F, Leavitt WD, Dahl C, Johnston DT, Pereira IA (December 2015). "A protein trisulfide couples dissimilatory sulfate reduction to energy conservation". Science. 350 (6267): 1541–5. Bibcode:2015Sci...350.1541S. doi:10.1126/science.aad3558. PMID 26680199. S2CID 206643054.
5. Venceslau SS, Stockdreher Y, Dahl C, Pereira IA (July 2014). "The "bacterial heterodisulfide" DsrC is a key protein in dissimilatory sulfur metabolism". Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1837 (7): 1148–64. doi:10.1016/j.bbabio.2014.03.007. PMID 24662917.

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