|Superclasses:||Reactions Classified By Conversion Type → Simple Reactions → Chemical Reactions|
|Reactions Classified By Substrate → Small-Molecule Reactions|
EC Number: 22.214.171.124
Enzymes and Genes:
|Homo sapiens:||hexaprenyldihydroxybenzoate methyltransferase: COQ3|
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: 3-demethylubiquinol 3-O-methyltransferase
Enzyme Commission Synonyms: 5-demethylubiquinone-9 methyltransferase, OMHMB-methyltransferase, 2-octaprenyl-3-methyl-5-hydroxy-6-methoxy-1,4-benzoquinone methyltransferase, S-adenosyl-L-methionine:2-octaprenyl-3-methyl-5-hydroxy-6-methoxy-1,4-benzoquinone-O-methyltransferase, COQ3 (gene name), Coq3 O-methyltransferase, ubiG (gene name, ambiguous)
Standard Gibbs Free Energy (ΔrG'° in kcal/mol): -4.3598633 [Latendresse13]
Enzyme Commission Summary:
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 [Poon99].
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)
Houser77: Houser RM, Olson RE (1977). "5-demethylubiquinone-9-methyltransferase from rat liver mitochondria. Characterization, localization, and solubilization." J Biol Chem 252(12);4017-21. PMID: 863914
Jonassen00: Jonassen T, Clarke CF (2000). "Isolation and functional expression of human COQ3, a gene encoding a methyltransferase required for ubiquinone biosynthesis." J Biol Chem 275(17);12381-7. PMID: 10777520
Leppik76: Leppik RA, Stroobant P, Shineberg B, Young IG, Gibson F (1976). "Membrane-associated reactions in ubiquinone biosynthesis. 2-Octaprenyl-3-methyl-5-hydroxy-6-methoxy-1,4-benzoquinone methyltransferase." Biochim Biophys Acta 1976;428(1);146-56. PMID: 769831
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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