Reaction: S-adenosyl-L-methionine + 3-(all-trans-polyprenyl)benzene-1,2-diol = S-adenosyl-L-homocysteine + 2-methoxy-6-(all-trans-polyprenyl)phenol
For diagram of reaction, click here
Other name(s): ubiG (gene name, ambiguous); ubiG methyltransferase (ambiguous); 2-octaprenyl-6-hydroxyphenol methylase
Systematic name: S-adenosyl-L-methionine:3-(all-trans-polyprenyl)benzene-1,2-diol 2-O-methyltransferase
Comments: UbiG catalyses both methylation steps in ubiquinone biosynthesis in Escherichia coli. The second methylation is classified as EC 18.104.22.168 (3-demethylubiquinol 3-O-methyltransferase) . In eukaryotes Coq3 catalyses the two methylation steps in ubiquinone biosynthesis. However, while the second methylation is common to both enzymes, the first methylation by Coq3 occurs at a different position within the pathway, and thus involves a different substrate and is classified as EC 22.214.171.124 (polyprenyldihydroxybenzoate methyltransferase). The substrate of the eukaryotic enzyme (3,4-dihydroxy-5-all-trans-polyprenylbenzoate) differs by an additional carboxylate moiety.
Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, CAS registry number:
1. Poon, W.W., Barkovich, R.J., Hsu, A.Y., Frankel, A., Lee, P.T., Shepherd, J.N., Myles, D.C. and 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 (1999) 21665-21672. [PMID: 10419476]
2. Hsu, A.Y., Poon, W.W., Shepherd, J.A., Myles, D.C. and Clarke, C.F. Complementation of coq3 mutant yeast by mitochondrial targeting of the Escherichia coli UbiG polypeptide: evidence that UbiG catalyzes both O-methylation steps in ubiquinone biosynthesis. Biochemistry 35 (1996) 9797-9806. [PMID: 8703953]