MetaCyc Enzyme: 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.

Gene-Reaction Schematic: ?

Gene-Reaction Schematic

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

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

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 reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, 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:

Km (μM)
an oxidized c-type cytochrome

T(opt): 65 °C [Kappler00]

pH(opt): 8 [Kappler00]

Subunit of sulfite dehydrogenase: sulfite:cytochrome c oxidoreductase molybdenum subunit

Synonyms: SorA

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

Molecular Weight: 43.4 kD (from nucleotide sequence)

Molecular Weight: 40.6 kD (experimental) [Kappler00]

Unification Links: Protein Model Portal:Q9LA16 , SMR:Q9LA16 , UniProt:Q9LA16

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

Subunit of sulfite dehydrogenase: sulfite:cytochrome c oxidoreductase cytochrome subunit

Synonyms: SorB

Gene: sorB Accession Number: G-9518 (MetaCyc)

Molecular Weight: 11.565 kD (from nucleotide sequence)

Molecular Weight: 8.8 kD (experimental) [Kappler00]

Unification Links: Protein Model Portal:Q9LA15 , SMR:Q9LA15 , UniProt:Q9LA15

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


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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