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A Canary's Eye View — Metabolic Basis
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Sulfite Oxidase

Catalyses the oxidation of sulfite to sulfate: necessary for metabolism of sulfur amino acids.

Deficiency is sulfocysteinuria, an autosomal recessive disorder.

  • Caused by mutation in gene SUOX (606887).
  • Inherited deficiency or absence commonly leads to death in infancy.
  • For people with mercury damage, who acquire it later, prognosis is unclear.
  • Tungsten can cause SO deficiency, by substituting for molybdenum. (See Human sulfite oxidase deficiency. Characterization of the molecular defect in a multicomponent system, by J L Johnson and K V Rajagopalan, from J Clin Invest. 1976 September; 58(3): 551–556.) In May 2005, a Doctors' Data stool test showed I was excreting 0.186 mg/kg tungsten (ref. range < 0.090). Note: remember to study xanthine oxidase too; tungsten does the same thing to that.
  • Mercury binds SO. If it’s bound, will it still show up in a blood test?
  • Does cadmium affect it? (In the Doctors' Data test my cadmium was 1.04 mg/kg, with a reference range of <.50)
  • Screening for SO deficiency?
    • In urine: increased sulfite, decreased inorganic sulfate
    • SO activity can be measured in fibroblasts.
    • Antibody specific for sulfite oxidase showing no crossreacting
    • Strip test: A simple test using a copper strip, originally developed for the semiquantitative determination of sulfite in wine and fruit juices. Available from Euroimmune; see catalog. Risk of false positives and false negatives.
    • A list (with links) of articles on several methods, on PubMed
    • A letter on the superiority of determining urinary thiosulfate/sulfate ratios by anion chromatography, (DE Cole & J. Evrovski, Clin Chem 1996 Apr;42(4):654-5)

Dysfunction can also be from molybdenum cofactor deficiency.


  • Increase SO? (How?)
  • Reduction of sulfur protein intake
    • Restrict protein from natural foods
    • And add a synthetic amino acid mixture without cystine and methionine (Xmet, Cys Maxamaid, SHS International Ltd).
    • See Dietary therapy in two patients with a mild form of sulphite oxidase deficiency. Evidence for clinical and biological improvement, by Touati G, Rusthoven E, Depondt E, Dorche C, Duran M, Heron B, Rabier D, Russo M, Saudubray JM, PubMed 10682307 from J Inherit Metab Dis. 2000 Feb;23(1):45-53.
  • Beat CFS and FMS, in their page on Sulfite Strategy, says supplementing these will help boost SO "a bit" and "in some cases."
    • Vitamin B1 - I've not tried
    • P5P (activated Vitamin B6) - currently can tolerate a very small amount
    • Vitamin B12 [needs fixing]
    • Molybdenum:
      • Great Smokies Elemental Analysis indicated my molybdenum is within reference range, but if I've got a lot of tungsten in me it could decrease the effectiveness of the molybdenum.
      • See Human sulfite oxidase deficiency. (ibid.)
    • Tetrahydrofolate - [could use folic acid or folinic acid?]

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Last updated 8 June 2007