EC - 3-demethylubiquinol 3-O-methyltransferase

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IntEnz Enzyme Nomenclature


Accepted name:
3-demethylubiquinol 3-O-methyltransferase
Other names:
2-octaprenyl-3-methyl-5-hydroxy-6-methoxy-1,4-benzoquinone methyltransferase
5-demethylubiquinone-9 methyltransferase
Coq3 O-methyltransferase
ubiG [ambiguous]
3-demethylubiquinone-9 3-methyltransferase
Systematic name:
S-adenosyl-L-methionine:3-hydroxy-2-methoxy-5-methyl-6-(all-trans-polyprenyl)-1,4-benzoquinol 3-O-methyltransferase



This enzyme is involved in ubiquinone biosynthesis. Ubiquinones from different organisms have a different number of prenyl units (for example, ubiquinone-6 in Saccharomyces, ubiquinone-9 in rat and ubiquinone-10 in human), and thus the natural substrate for the enzymes from different organisms has a different number of prenyl units. However, the enzyme usually shows a low degree of specificity regarding the number of prenyl units. For example, the human COQ3 enzyme can restore biosynthesis of ubiquinone-6 in coq3 deletion mutants of yeast [3]. The enzymes from yeast, Escherichia coli and rat also catalyse the methylation of 3,4-dihydroxy-5-all-trans-polyprenylbenzoate [3] (a reaction that is classified as EC, polyprenyldihydroxybenzoate methyltransferase).

Links to other databases

Enzymes and pathways: NC-IUBMB , BRENDA , DIAGRAM , ERGO , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , UniPathway
Structural data: CSA , EC2PDB
Gene Ontology: GO:0008689
CAS Registry Number: 63774-48-1
UniProtKB/Swiss-Prot: (253) [show] [UniProt]


  1. Houser, R.M. and Olson, R.E.
    5-Demethylubiquinone-9-methyltransferase from rat liver mitochondria. Characterization, localization, and solubilization.
    J. Biol. Chem. 252 : 4017-4021 (1977). [PMID: 863914]
  2. Leppik, R.A., Stroobant, P., Shineberg, B., Young, I.G. and Gibson, F.
    Membrane-associated reactions in ubiquinone biosynthesis. 2-Octaprenyl-3-methyl-5-hydroxy-6-methoxy-1,4-benzoquinone methyltransferase.
    Biochim. Biophys. Acta 428 : 146-156 (1976). [PMID: 769831]
  3. Poon, W. W., Barkovich, R. J., Hsu, A. Y., Frankel, A., Lee, P. T., Shepherd, J. N., Myles, D. C., Clarke, C. F.
    Yeast and rat Coq3 and Escherichia coli UbiG polypeptides catalyze both O-methyltransferase steps in coenzyme Q biosynthesis.
    J. Biol. Chem. 274 : 21665-21672 (1999). [PMID: 10419476]
  4. Jonassen, T., Clarke, C. F.
    Isolation and functional expression of human COQ3, a gene encoding a methyltransferase required for ubiquinone biosynthesis.
    J. Biol. Chem. 275 : 12381-12387 (2000). [PMID: 10777520]

[EC created 1982, modified 2011]