dissimilatory sulfite reductase | |
Ec Number: | 1.8.99.5 |
Go Code: | 0016002 |
Pdb: | 2V4J, 3MM5 |
Dissimilatory sulfite reductase is an enzyme that participates in sulfur metabolism in dissimilatory sulfate reduction.[1]
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:
(1) sulfite + a [DsrC protein]-dithiol + 2 reduced acceptor + 2 H+ = hydrogen sulfide + a [DsrC protein]-disulfide + 2 acceptor + 3 H2O (overall reaction)
(1a) sulfite + a [DsrC protein]-dithiol + 2 reduced acceptor + 2 H+ = a [DsrC protein]-S-sulfanyl-L-cysteine + 2 acceptor + 3 H2O
(1b) a [DsrC protein]-S-sulfanyl-L-cysteine = hydrogen sulfide + a [DsrC protein]-disulfide
Reaction in organisms performing sulfur oxidation:
(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
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.