ExplorEnz: EC 1.8.99.5

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1.8.99.5

Accepted name:

dissimilatory sulfite reductase

Reaction:

(1) hydrogen sulfide + a [DsrC protein]-disulfide + 2 acceptor + 3 H₂O = sulfite + a [DsrC protein]-dithiol + 2 reduced acceptor + 2 H⁺ (overall reaction)
(1a) hydrogen sulfide + a [DsrC protein]-disulfide = a [DsrC protein]-S-sulfanyl-L-cysteine
(1b) a [DsrC protein]-S-sulfanyl-L-cysteine + 2 acceptor + 3 H₂O = sulfite + a [DsrC protein]-dithiol + 2 reduced acceptor + 2 H⁺
(2) a [DsrC protein]-S-sulfanyl-L-cysteine + 3 acceptor + 3 H₂O = sulfite + a [DsrC protein]-disulfide + 3 reduced acceptor + 2 H⁺ (overall reaction)
(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

Other name(s):

siroheme sulfite reductase; hydrogen-sulfide:(acceptor) oxidoreductase (ambiguous); DsrAB

Systematic name:

hydrogen-sulfide:[DsrC sulfur-carrier protein],acceptor oxidoreductase

Comments:

Contain siroheme. 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 in the right to left direction), while in sulfur oxidizers it catalyses the opposite reaction (reaction 2 in the left to right direction) [1]. The reaction involves the small protein DsrC, which is present in all the organisms that contain dissimilatory sulfite reductase. During the process an intramolecular disulfide bond is formed between two L-cysteine residues of DsrC. This disulfide can be reduced by a number of proteins including DsrK and TcmB [5]. 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.

Links to other databases:

BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 37256-51-2

References:

1.	Schedel, M., Vanselow, M. and Trueper, H. G. Siroheme sulfite reductase from Chromatium vinosum. Purification and investigation of some of its molecular and catalytic properties. Arch. Microbiol. 121 (1979) 29–36.
2.	Seki, Y., Sogawa, N. and Ishimoto, M. Siroheme as an active catalyst in sulfite reduction. J. Biochem. 90 (1981) 1487–1492. [PMID: 7338517]
3.	Pott, A.S. and Dahl, C. Sirohaem sulfite reductase and other proteins encoded by genes at the dsr locus of Chromatium vinosum are involved in the oxidation of intracellular sulfur. Microbiology 144 (1998) 1881–1894. [DOI] [PMID: 9695921]
4.	Oliveira, T.F., Vonrhein, C., Matias, P.M., Venceslau, S.S., Pereira, I.A. and Archer, M. The crystal structure of Desulfovibrio vulgaris dissimilatory sulfite reductase bound to DsrC provides novel insights into the mechanism of sulfate respiration. J. Biol. Chem. 283 (2008) 34141–34149. [DOI] [PMID: 18829451]
5.	Venceslau, S.S., Stockdreher, Y., Dahl, C. and Pereira, I.A. The "bacterial heterodisulfide" DsrC is a key protein in dissimilatory sulfur metabolism. Biochim. Biophys. Acta 1837 (2014) 1148–1164. [DOI] [PMID: 24662917]

[EC 1.8.99.5 created 2015]