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MetaCyc Compound Class: a ubiquinone

Abbrev Name: UQ

Synonyms: coenzyme-Qn, ubiquinone, Q

Superclasses: an acceptor a redox electron carrier Membrane-Electron-Carriers an electron-transfer quinone
an aldehyde or ketone a ketone a cyclic ketone a quinone an electron-transfer quinone

Summary:
The ubiquinones are a group of lipid-soluble benzoquinones involved in electron transport. Their structures have a variable length side chain, which consists of one to twelve mono-unsaturated trans-isoprenoids units, with ten units being the most common in animals. Saccharomyces cerevisiae has 6 units, Haemophilus influenzae Rd KW20 has 7, Escherichia coli K-12 has 8, Synechocystis has 9, Homo sapiens has 10, and Micrococcus luteus has an 11 unit form [Kawamukai02].

The terms ubiquinone/ubiquinol refer to the oxidized/reduced forms, and are often used interchangeably. The forms are readily interconvertable.

Ubiquinone is also known as coenzyme Q, or just Q. The names are often followed by the number of the prenoid units in the side chain (e.g. Q-8), or the number of carbons in the chain. For example, the name Q-8 may be substituted with ubiiquinone(40). Since these carbons occur in repeating units of five, these number are multiples of 5.

a ubiquinone compound structure

Instances:
ubiquinone-0 ,
ubiquinone-1 ,
ubiquinone-2 ,
ubiquinone-4 ,
ubiquinone-6 ,
ubiquinone-7 ,
ubiquinone-8 ,
ubiquinone-9 ,
ubiquinone-10

SMILES: C([R])C(C)=CCC1(=C(C)C(=O)C(OC)=C(OC)C(=O)1)

Unification Links: ChEBI:16389 , KEGG:C00399

Reactions known to consume the compound:

2-chloroacrylate degradation I , D-lactate to cytochrome bo oxidase electron transport , methylglyoxal degradation I , methylglyoxal degradation II :
(R)-lactate + a ubiquinone[inner membrane] → pyruvate + an ubiquinol[inner membrane]

aerobic respiration I (cytochrome c) , aerobic respiration III (alternative oxidase pathway) , methylaspartate cycle , succinate to cytochrome bd oxidase electron transfer , succinate to cytochrome bo oxidase electron transfer , superpathway of glyoxylate cycle and fatty acid degradation , TCA cycle I (prokaryotic) , TCA cycle II (plants and fungi) , TCA cycle III (animals) :
succinate[in] + a ubiquinone[membrane] → fumarate[in] + an ubiquinol[membrane]

aerobic respiration II (cytochrome c) (yeast) :
NADH[in] + a ubiquinone[membrane] + H+[in] → NAD+[in] + an ubiquinol[membrane]
succinate[in] + a ubiquinone[membrane] → fumarate[in] + an ubiquinol[membrane]

caffeine degradation V (bacteria, via trimethylurate) :
caffeine + a ubiquinone + H2O → 1,3,7-trimethylurate + an ubiquinol

Fe(II) oxidation :
2 a reduced CycA1 cytochrome[periplasmic space] + a ubiquinone[inner membrane] + 4 H+ → 2 an oxidized CycA1 cytochrome[periplasmic space] + an ubiquinol[inner membrane] + 2 H+[periplasmic space]

glucose and glucose-1-phosphate degradation , glucose degradation (oxidative) , L-ascorbate biosynthesis VI (engineered pathway) :
D-glucopyranose[periplasmic space] + a ubiquinone[inner membrane] → D-glucono-1,5-lactone[periplasmic space] + an ubiquinol[inner membrane]

glycerol degradation I , glycerol-3-phosphate shuttle , glycerol-3-phosphate to cytochrome bo oxidase electron transfer , glycerophosphodiester degradation , nitrate reduction X (periplasmic, dissimilatory) :
sn-glycerol 3-phosphate[in] + a ubiquinone[membrane] → glycerone phosphate[in] + an ubiquinol[membrane]

NAD/NADP-NADH/NADPH mitochondrial interconversion (yeast) , NADH to cytochrome bd oxidase electron transport II , NADH to cytochrome bo oxidase electron transfer II :
NADH[in] + a ubiquinone[membrane] + H+[in] → NAD+[in] + an ubiquinol[membrane]

proline to cytochrome bo oxidase electron transfer :
L-proline + a ubiquinone[inner membrane] → (S)-1-pyrroline-5-carboxylate + an ubiquinol[inner membrane] + H+

pyruvate to cytochrome bd terminal oxidase electron transfer , pyruvate to cytochrome bo oxidase electron transfer :
pyruvate + a ubiquinone[inner membrane] + H2O → CO2 + acetate + an ubiquinol[inner membrane]

Not in pathways:
β-D-glucopyranose[periplasmic space] + a ubiquinone[inner membrane] → D-glucono-1,5-lactone[periplasmic space] + an ubiquinol[inner membrane]
L-proline[in] + a ubiquinone[membrane] → (S)-1-pyrroline-5-carboxylate[in] + an ubiquinol[membrane] + H+[in]
a reduced electron-transfer flavoprotein[mitochondrial lumen] + a ubiquinone[mitochondrial inner membrane] → an oxidized electron-transfer flavoprotein[mitochondrial lumen] + an ubiquinol[mitochondrial inner membrane] + H+[mitochondrial lumen]
(S)-dihydroorotate[in] + a ubiquinone[membrane] → orotate[in] + an ubiquinol[membrane]

(5R)-carbapenem carboxylate biosynthesis , L-citrulline biosynthesis , L-Nδ-acetylornithine biosynthesis , L-proline degradation :
L-proline + an electron-transfer quinone[inner membrane] → (S)-1-pyrroline-5-carboxylate + an electron-transfer quinol[inner membrane] + H+

4-hydroxymandelate degradation :
(S)-4-hydroxymandelate + an electron-transfer quinone → 2-(4-hydroxyphenyl)-2-oxoacetate + an electron-transfer quinol

L-alanine degradation I :
D-alanine + an electron-transfer quinone[inner membrane] + H2O → ammonium + pyruvate + an electron-transfer quinol[inner membrane]

sulfide oxidation I (sulfide-quinone reductase) :
hydrogen sulfide + an electron-transfer quinone → intracellular S0 + an electron-transfer quinol

TCA cycle I (prokaryotic) :
(S)-malate + an electron-transfer quinone[inner membrane] → oxaloacetate + an electron-transfer quinol[inner membrane]

TCA cycle IV (2-oxoglutarate decarboxylase) , TCA cycle V (2-oxoglutarate:ferredoxin oxidoreductase) :
succinate[in] + an electron-transfer quinone[membrane] → fumarate[in] + an electron-transfer quinol[membrane]

TCA cycle VII (acetate-producers) :
succinate[in] + an electron-transfer quinone[membrane] → fumarate[in] + an electron-transfer quinol[membrane]
(S)-malate + an electron-transfer quinone[inner membrane] → oxaloacetate + an electron-transfer quinol[inner membrane]

trans-4-hydroxy-L-proline degradation I :
trans-4-hydroxy-L-proline[in] + an electron-transfer quinone[membrane] → (3R,5S)-1-pyrroline-3-hydroxy-5-carboxylate[in] + an electron-transfer quinol[membrane] + H+[in]

trans-lycopene biosynthesis II (plants) :
9,9'-di-cis-ζ-carotene + an electron-transfer quinone → 7,9,9'-cis-neurosporene + an electron-transfer quinol

Reactions known to produce the compound:

aerobic respiration III (alternative oxidase pathway) :
2 an ubiquinol[mitochondrial inner membrane] + oxygen[mitochondrial lumen] → 2 a ubiquinone[mitochondrial inner membrane] + 2 H2O[mitochondrial lumen]

D-lactate to cytochrome bo oxidase electron transport , glycerol-3-phosphate to cytochrome bo oxidase electron transfer , NADH to cytochrome bo oxidase electron transfer I , NADH to cytochrome bo oxidase electron transfer II , proline to cytochrome bo oxidase electron transfer , pyruvate to cytochrome bo oxidase electron transfer , succinate to cytochrome bo oxidase electron transfer :
2 an ubiquinol[inner membrane] + oxygen + 5 H+ → 2 a ubiquinone[inner membrane] + 2 H2O + 5 H+[periplasmic space]

long chain fatty acid ester synthesis for microdiesel production :
ethanol + a ubiquinone ← acetaldehyde + an ubiquinol

NADH to cytochrome bd oxidase electron transfer I , NADH to cytochrome bd oxidase electron transport II , pyruvate to cytochrome bd terminal oxidase electron transfer , succinate to cytochrome bd oxidase electron transfer :
2 an ubiquinol[inner membrane] + 4 H+ + oxygen → 2 a ubiquinone[inner membrane] + 4 H+[periplasmic space] + 2 H2O

nitrate reduction X (periplasmic, dissimilatory) :
nitrate[periplasmic space] + an ubiquinol[inner membrane] → nitrite[periplasmic space] + a ubiquinone[inner membrane] + H2O[periplasmic space]

Not in pathways:
nitrate + an ubiquinol[inner membrane] + 2 H+ → nitrite + a ubiquinone[inner membrane] + 2 H+[periplasmic space] + H2O

methane oxidation to methanol II :
methane + an electron-transfer quinol + oxygen → methanol + an electron-transfer quinone + H2O

TCA cycle VI (obligate autotrophs) :
succinate[in] + an electron-transfer quinone[membrane] ← fumarate[in] + an electron-transfer quinol[membrane]

Not in pathways:
2 an oxidized c-type cytochrome[out] + an electron-transfer quinol[membrane] → 2 a reduced c-type cytochrome[out] + an electron-transfer quinone[membrane] + 2 H+[in]

cuticular wax biosynthesis :
a secondary alcohol + an oxidized unknown electron acceptor → a ketone + an reduced unknown electron acceptor

Not in pathways:
a secondary alcohol + oxygen → a ketone + hydrogen peroxide

Not in pathways:
a nitroalkane + oxygen + H2O → an aldehyde or ketone + nitrite + hydrogen peroxide + H+

Reactions known to both consume and produce the compound:

aerobic respiration I (cytochrome c) :
2 an oxidized c-type cytochrome[out] + an ubiquinol[membrane] ↔ 2 a reduced c-type cytochrome[out] + a ubiquinone[membrane] + 2 H+[out]
NADH[in] + a ubiquinone[membrane] + 5 H+[in] ↔ NAD+[in] + an ubiquinol[membrane] + 4 H+[out]

aerobic respiration II (cytochrome c) (yeast) , ammonia oxidation IV (autotrophic ammonia oxidizers) :
2 an oxidized c-type cytochrome[out] + an ubiquinol[membrane] ↔ 2 a reduced c-type cytochrome[out] + a ubiquinone[membrane] + 2 H+[out]

aerobic respiration III (alternative oxidase pathway) , Fe(II) oxidation , NAD/NADH phosphorylation and dephosphorylation , NADH to cytochrome bd oxidase electron transfer I , NADH to cytochrome bo oxidase electron transfer I :
NADH[in] + a ubiquinone[membrane] + 5 H+[in] ↔ NAD+[in] + an ubiquinol[membrane] + 4 H+[out]

nitrate reduction I (denitrification) , nitrate reduction VII (denitrification) :
nitrate + an electron-transfer quinol[inner membrane] ↔ nitrite + an electron-transfer quinone[inner membrane] + H2O

Not in pathways:
2 a quinone + NADPH + H+ ↔ 2 a semiquinone + NADP+

In Reactions of unknown directionality:

Not in pathways:
a reduced electron-transfer flavoprotein + a ubiquinone = an oxidized electron-transfer flavoprotein + an ubiquinol + H+
D-proline + a ubiquinone = 1-pyrroline-2-carboxylate + an ubiquinol + H+

Not in pathways:
9,9'-di-cis-ζ-carotene + 2 an electron-transfer quinone = prolycopene + 2 an electron-transfer quinol
formate + an electron-transfer quinone + H+ = CO2 + an electron-transfer quinol
an (R)-2-hydroxyacid + an electron-transfer quinone = a 2-oxo acid + an electron-transfer quinol
an aldehyde + an electron-transfer quinone + H2O = a carboxylate + an electron-transfer quinol + H+
NADH + an electron-transfer quinone + H+ = NAD+ + an electron-transfer quinol
an oxidized coenzyme F420 + an electron-transfer quinol = a reduced coenzyme F420 + an electron-transfer quinone

Not in pathways:
2 a quinone + NADH + H+ = 2 a semiquinone + NAD+
1-(β-D-ribofuranosyl)-1,4-dihydronicotinamide + a quinone + H+ = a quinol + 1-(β-D ribofuranosyl)nicotinamide

Not in pathways:
a ketone + NADP+ = an enone + NADPH + H+
a secondary alcohol + an oxidized coenzyme F420 = a ketone + a reduced coenzyme F420
a secondary alcohol + NADP+ = a ketone + NADPH + H+
a secondary alcohol + NAD+ = a ketone + NADH + H+

In Transport reactions:
Na+[in] + NADH + a ubiquinone + H+ → Na+[out] + NAD+ + an ubiquinol

In Redox half-reactions:
a ubiquinone[membrane] + 2 H+[in] + 2 e-[membrane] → an ubiquinol[membrane] ,
a ubiquinone[membrane] + 2 H+[out] + 2 e-[membrane] → an ubiquinol[membrane] ,
an electron-transfer quinone[membrane] + 2 H+[in] + 2 e-[membrane] → an electron-transfer quinol[membrane]

This compound has been characterized as a cofactor or prosthetic group of the following enzymes: putrescine oxidase

Credits:
Revised 17-Aug-2009 by Caspi R , SRI International


References

Kawamukai02: Kawamukai M (2002). "Biosynthesis, bioproduction and novel roles of ubiquinone." J Biosci Bioeng 94(6);511-7. PMID: 16233343


Report Errors or Provide Feedback
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 Tue Sep 1, 2015, biocyc13.