MetaCyc Reaction:

Superclasses: Reactions Classified By Conversion Type Simple Reactions Chemical Reactions
Reactions Classified By Substrate Small-Molecule Reactions

EC Number:

Enzymes and Genes:

Escherichia coli K-12 substr. MG1655 : bifunctional 3-demethylubiquinone-8 3-O-methyltransferase and 2-octaprenyl-6-hydroxyphenol methylase Inferred from experiment : ubiG
Homo sapiens : hexaprenyldihydroxybenzoate methyltransferase : COQ3

In Pathway: ubiquinol-8 biosynthesis (prokaryotic)

Note that this reaction equation differs from the official Enzyme Commission reaction equation for this EC number, which can be found here .

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction in which it was curated.

Most BioCyc compounds have been protonated to a reference pH value of 7.3, and some reactions have been computationally balanced for hydrogen by adding free protons. Please see the PGDB Concepts Guide for more information.

Mass balance status: Balanced.

Direct generic reaction:
a 3-(all-trans-polyrenyl)benzene-1,2-diol + S-adenosyl-L-methionine → a 2-methoxy-6-(all-trans-polyprenyl)phenol + S-adenosyl-L-homocysteine + H+ (

Enzyme Commission Primary Name: 2-polyprenyl-6-hydroxyphenol methylase

Enzyme Commission Synonyms: ubiG (gene name, ambiguous), ubiG methyltransferase (ambiguous), 2-octaprenyl-6-hydroxyphenol methylase

Standard Gibbs Free Energy (ΔrG in kcal/mol): -4.359993 Inferred by computational analysis [Latendresse13]

The enzyme is involved in the pathway of ubiquinone-8 in Escherichia coli. COQ3 from human, yeast and rat also catalyse the reaction although this is not a step in biosynthesis of ubiquinone in these organisms [Poon99]. The enzyme also catalyses the methylation of 3-demethylubiquinone-8 (this activity is classified as EC [Hsu96a].

Enzyme Commission Summary:
UbiG catalyses both methylation steps in ubiquinone biosynthesis in Escherichia coli. The second methylation is classified as EC (3-demethylubiquinol 3-O-methyltransferase) [Hsu96a]. 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 (polyprenyldihydroxybenzoate methyltransferase). The substrate of the eukaryotic enzyme (3,4-dihydroxy-5-all-trans-polyprenylbenzoate) differs by an additional carboxylate moiety.

Gene-Reaction Schematic: ?

Gene-Reaction Schematic

Instance reactions of [a 3-(all-trans-polyrenyl)benzene-1,2-diol + S-adenosyl-L-methionine → a 2-methoxy-6-(all-trans-polyprenyl)phenol + S-adenosyl-L-homocysteine + H+] (
i1: 3-(all-trans-nonaprenyl)benzene-1,2-diol + S-adenosyl-L-methionine → 2-methoxy-6-(all-trans-nonaprenyl)phenol + S-adenosyl-L-homocysteine + H+ (

i2: 3-(all-trans-decaprenyl)benzene-1,2-diol + S-adenosyl-L-methionine → 2-methoxy-6-(all-trans-decaprenyl)phenol + S-adenosyl-L-homocysteine + H+ (

i3: 3-(all-trans-heptaprenyl)benzene-1,2-diol + S-adenosyl-L-methionine → 2-methoxy-6-(all-trans-heptaprenyl)phenol + S-adenosyl-L-homocysteine + H+ (

i4: 3-(all-trans-octaprenyl)benzene-1,2-diol + S-adenosyl-L-methionine → 2-methoxy-6-(all-trans-octaprenyl)phenol + S-adenosyl-L-homocysteine + H+ (

Unification Links: KEGG:R04988 , Rhea:27770

Relationship Links: BRENDA:EC: , ENZYME:EC: , IUBMB-ExplorEnz:EC:

Revised 11-Oct-2010 by Caspi R , SRI International


Hsu96a: Hsu AY, Poon WW, Shepherd JA, Myles DC, Clarke CF (1996). "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 1996;35(30);9797-806. PMID: 8703953

Latendresse13: Latendresse M. (2013). "Computing Gibbs Free Energy of Compounds and Reactions in MetaCyc."

Poon99: Poon WW, Barkovich RJ, Hsu AY, Frankel A, Lee PT, Shepherd JN, Myles DC, Clarke CF (1999). "Yeast and rat Coq3 and Escherichia coli UbiG polypeptides catalyze both O-methyltransferase steps in coenzyme Q biosynthesis." J Biol Chem 274(31);21665-72. PMID: 10419476

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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
Page generated by SRI International Pathway Tools version 19.0 on Fri May 22, 2015, biocyc14.