EC - Polyprenyldihydroxybenzoate methyltransferase

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IntEnz Enzyme Nomenclature


Accepted name:
polyprenyldihydroxybenzoate methyltransferase
Other names:
3,4-dihydroxy-5-hexaprenylbenzoate methyltransferase
dihydroxyhexaprenylbenzoate methyltransferase
DHHB methyltransferase
Coq3 O-methyltransferase
DHHB O-methyltransferase
Systematic name:
S-adenosyl-L-methionine:3,4-dihydroxy-5-all-trans-polyprenylbenzoate 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 and rat also catalyse the methylation of 3-demethylubiquinol-6 and 3-demethylubiquinol-9, respectively [2] (this activity is classified as EC, 3-demethylubiquinol 3-O-methyltransferase).

Links to other databases

Enzymes and pathways: NC-IUBMB , BRENDA , DIAGRAM , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , UniPathway
Structural data: CSA , EC2PDB
Gene Ontology: GO:0010420 , GO:0004395
CAS Registry Number: 139569-30-5


  1. Clarke, C.F., Williams, W. and Teruya, J.H.
    Ubiquinone biosynthesis in Saccharomyces cerevisiae. Isolation and sequence of COQ3, the 3,4-dihydroxy-5-hexaprenylbenzoate methyltransferase gene.
    J. Biol. Chem. 266 : 16636-16641 (1991). [PMID: 1885593]
  2. 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]
  3. 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]
  4. Xing, L., Zhu, Y., Fang, P., Wang, J., Zeng, F., Li, X., Teng, M., Li, X.
    Crystallization and preliminary crystallographic studies of UbiG, an O-methyltransferase from Escherichia coli.
    Acta Crystallogr. Sect. F Struct. Biol. Cryst. Commun. 67 : 727-729 (2011). [PMID: 21636923]

[EC created 1999]