MetaCyc Polypeptide: sulfite:cytochrome c oxidoreductase molybdenum subunit

Gene: sorA Accession Number: G-9517 (MetaCyc)

Species: Starkeya novella

Component of: sulfite dehydrogenase (extended summary available)

Molecular Weight of Polypeptide: 43.4 kD (from nucleotide sequence), 40.6 kD (experimental) [Kappler00]

Unification Links: Protein Model Portal:Q9LA16, SMR:Q9LA16, String:639283.Snov_3268, UniProt:Q9LA16

Relationship Links: Entrez-Nucleotide:RELATED-TO:AF154565, 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-Reaction Schematic

Gene-Reaction Schematic

Subunit of: sulfite dehydrogenase

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.

Created 21-Aug-2006 by Caspi R, SRI International

Enzymatic reaction of: sulfite:cytochrome c oxidoreductase (sulfite dehydrogenase)

Inferred from experiment

Synonyms: sulfite oxidase, SOR, sulfite:cytochrome c reductase

EC Number:

sulfite + 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.

In Pathways: superpathway of sulfide oxidation (Starkeya novella), sulfite oxidation I (sulfite oxidoreductase)

Cofactors or Prosthetic Groups: heme d, heme [Toghrol83], Mo2+ [Toghrol83]

Inhibitors (Noncompetitive): sulfate [Kappler00]Kinetic Parameters:
Substrate Km (μM) Citations
an oxidized c-type cytochrome 4.0 [Kappler00]
sulfite 27.0 [Kappler00]

T(opt): 65 °C [Kappler00]

pH(opt): 8 [Kappler00]


Ambler91: Ambler RP (1991). "Sequence variability in bacterial cytochromes c." Biochim Biophys Acta 1058(1);42-7. PMID: 1646017

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

Toghrol83: Toghrol F, Southerland WM (1983). "Purification of Thiobacillus novellus sulfite oxidase. Evidence for the presence of heme and molybdenum." J Biol Chem 258(11);6762-6. PMID: 6853504

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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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
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