Species: Starkeya novella
Subunit composition of
sulfite dehydrogenase = [SorA][SorB]
sulfite:cytochrome c oxidoreductase molybdenum subunit = SorA
sulfite:cytochrome c oxidoreductase cytochrome subunit = SorB
The SorAB protein from the α-proteobacterium Starkeya novella is the best characterized soluble, complex-independent sulfite:acceptor oxidoreductase. It is a heterodimer, with a large subunit that binds a molybdopyranopterin cofactor and a smaller monoheme cytochrome c subunit [Kappler00].
During catalysis electrons are transferred to the single heme c552 located on the smaller subunit, and passed to a cytochrome c550 which is believed to be the enzyme's natural electron acceptor [Yamanaka81]. The enzyme exhibits a Ping Pong mechanism (similarly to eukaryotic SORs), and is non-competitively inhibited by sulfate. A structure revealed that the short distance between the two redox centers in the protein complex allows for rapid electron transfer via tunnelling. A potential site of electron transfer to an external acceptor cytochrome c was identified on the SorB subunit [Kappler05].
The sorAB genes encoding the enzyme form an operon by themselves.
Enzymatic reaction of: sulfite:cytochrome c oxidoreductase (sulfite dehydrogenase)
Synonyms: sulfite oxidase, SOR, sulfite:cytochrome c reductase
EC Number: 18.104.22.168sulfite + 2 an oxidized c-type cytochrome + H2O → sulfate + 2 a reduced c-type cytochrome + 2 H+
The direction shown, i.e. which substrates are on the left and right sides, is in accordance with the Enzyme Commission system.
The reaction is favored in the direction shown.sulfate [Kappler00]Kinetic Parameters:
|an oxidized c-type cytochrome||4.0||[Kappler00]|
T(opt): 65 °C [Kappler00]
pH(opt): 8 [Kappler00]
|Gene:||sorA||Accession Number: G-9517 (MetaCyc)|
Molecular Weight: 43.4 kD (from nucleotide sequence)
Molecular Weight: 40.6 kD (experimental) [Kappler00]
Relationship Links: InterPro:IN-FAMILY:IPR000572, InterPro:IN-FAMILY:IPR005066, InterPro:IN-FAMILY:IPR006311, InterPro:IN-FAMILY:IPR008335, InterPro:IN-FAMILY:IPR014756, PDB:Structure:2BLF, PDB:Structure:2BPB, PDB:Structure:2C9X, PDB:Structure:2CA3, PDB:Structure:2CA4, Pfam:IN-FAMILY:PF00174, Pfam:IN-FAMILY:PF03404, Prints:IN-FAMILY:PR00407, Prosite:IN-FAMILY:PS51318
|Gene:||sorB||Accession Number: G-9518 (MetaCyc)|
Molecular Weight: 11.565 kD (from nucleotide sequence)
Molecular Weight: 8.8 kD (experimental) [Kappler00]
Relationship Links: InterPro:IN-FAMILY:IPR002326, InterPro:IN-FAMILY:IPR009056, PDB:Structure:2BLF, PDB:Structure:2BPB, PDB:Structure:2C9X, PDB:Structure:2CA3, PDB:Structure:2CA4, Pfam:IN-FAMILY:PF02167
Kappler00: Kappler U, Bennett B, Rethmeier J, Schwarz G, Deutzmann R, McEwan AG, Dahl C (2000). "Sulfite:Cytochrome c oxidoreductase from Thiobacillus novellus. Purification, characterization, and molecular biology of a heterodimeric member of the sulfite oxidase family." J Biol Chem 275(18);13202-12. PMID: 10788424
Kappler05: Kappler U, Bailey S (2005). "Molecular basis of intramolecular electron transfer in sulfite-oxidizing enzymes is revealed by high resolution structure of a heterodimeric complex of the catalytic molybdopterin subunit and a c-type cytochrome subunit." J Biol Chem 280(26);24999-5007. PMID: 15863498
Yamanaka81: Yamanaka, T., Yoshioka, T., Kimura, K. (1981). "Purification of sulphite cytocrome c reductase of Thiobacillus novellus and reconstitution of its sulphite oxidase system with the purified constituents." Plant and Cell Physiol.,22(4):631-622.
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