Overview for MACiE Entry M0121

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General Information

EC Number: (A member of the Oxidoreductases, Acting on a sulfur group of donors, With oxygen as acceptor)

Enzyme Name: sulfite oxidase

Biological Species: Gallus gallus (Chicken)

Catalytic Chain UniprotKB Accession Codes:

Representative PDB Code: 1sox - SULFITE OXIDASE FROM CHICKEN LIVER (Resolution = 1.90 Å).

Catalytic CATH Codes:

"Other" CATH Codes:

Display structure information

Overall Reaction:

Image of water

Image of ferricytochrome c

Image of sulphite

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Image of proton

Image of ferrocytochrome c

Image of sulphate

2 ferricytochrome c
2 proton
2 ferrocytochrome c

It is unknown whether this reaction is reversible or not.

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Stepwise Description of the Reaction

Step 1Sulfite initiates a nucleophilic attack upon one of the oxo groups coordinated to the Mo(VI) centre in an addition reaction, resulting in a two electron reduction of the centre to Mo(IV).
Step 2Water displaces the sulfate as a ligand to the Mo(IV) centre.
Step 3Water deprotonates Tyr322, which deprotonates the Mo-bound water causing a single electron to be transferred from the Mo(IV) centre to Haem and thence to ferricyrochrome C.
Step 4Water deprotonates Tyr322, which deprotonates the Mo-bound hydroxide causing a single electron to be transferred from the Mo(V) centre to Haem and thence to ferricyrochrome C and regenerating the cofactor.

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Catalytic Residues Involved

Type Number Chain Location of Function
Tyr 322 A Side Chain

Metal Cofactors for M0121

Type Het group Number Chain
molybdenum MO 505 A Overview
iron HEM 502 A Overview


  1. C. Feng et al. (2003), J. Biol. Chem., 278, 2913-2920. Role of conserved tyrosine 343 in intramolecular electron transfer in human sulfite oxidase.
    Medline: 12424234
  2. C. Kisker et al. (1997), Annu. Rev. Biochem., 66, 233-267. Molybdenum-cofactor-containing enzymes: structure and mechanism.
    Medline: 9242907

Homologue information for M0121 (1sox)

CSA Homologues

MACiE Homologues (within the PDB)

MACiE Homologues (within UniprotKB/SwissProt)

Links to this entry in other databases

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Link to EzCatDB

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binding (molecular function)
mitochondrion (cellular component)
mitochondrial intermembrane space (cellular component)
sulfite oxidase activity (molecular function)
electron carrier activity (molecular function)
oxidoreductase activity (molecular function)
heme binding (molecular function)
molybdenum ion binding (molecular function)
metal ion binding (molecular function)
oxidation-reduction process (biological process)