|Superclasses:||Reactions Classified By Conversion Type → Simple Reactions → Chemical Reactions|
|Reactions Classified By Substrate → Small-Molecule Reactions|
EC Number: 184.108.40.206
Enzymes and Genes:
|Escherichia coli K-12 substr. MG1655:||bifunctional 3-demethylubiquinone-8 3-O-methyltransferase and 2-octaprenyl-6-hydroxyphenol methylase: 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 direction shown, i.e. which substrates are on the left and right sides, 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. Please see the PGDB Concepts Guide for more information.
Mass balance status: Balanced.
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 [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 220.127.116.11) [Hsu96].
Enzyme Commission Summary:
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) [Hsu96]. 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.
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+] (126.96.36.199):
i1: 3-(all-trans-decaprenyl)benzene-1,2-diol + S-adenosyl-L-methionine → 2-methoxy-6-(all-trans-decaprenyl)phenol + S-adenosyl-L-homocysteine + H+ (188.8.131.52)
i2: 3-(all-trans-octaprenyl)benzene-1,2-diol + S-adenosyl-L-methionine → 2-methoxy-6-(all-trans-octaprenyl)phenol + S-adenosyl-L-homocysteine + H+ (184.108.40.206)
i3: 3-(all-trans-nonaprenyl)benzene-1,2-diol + S-adenosyl-L-methionine → 2-methoxy-6-(all-trans-nonaprenyl)phenol + S-adenosyl-L-homocysteine + H+ (220.127.116.11)
i4: 3-(all-trans-heptaprenyl)benzene-1,2-diol + S-adenosyl-L-methionine → 2-methoxy-6-(all-trans-heptaprenyl)phenol + S-adenosyl-L-homocysteine + H+ (18.104.22.168)
Hsu96: 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
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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