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MetaCyc Compound Class: a plastoquinone

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:
Plastoquinones (PQ) are benzoquinone electron carriers that can function as acceptor/donor for either one or two electrons. They are analogs of ubiquinones (Coenzyme Q), with two methyl groups substituting the methoxy groups found in Q. The fully reduced form is called a plastoquinol.

Plastoquinones are found in the chloroplasts of higher plants, red, brown and green algae, and in cyanobacteria, and are important members of the photosynthetic electron transfer chain, where they carry electrons from photosystem II to the cytochrome b6f complex. Plastoquinones also serve as cofactors involved in the desaturation of phytoene in the synthesis of carotenoids (see trans-lycopene biosynthesis II (plants)).

Plastoquinone was isolated originally in 1946 from alfalfa, but was not identified at the time. It was rediscovered in 1959 and its structure was described in the same year (see [Collins81]).

Please note that tyhe structure shown here is that of plastoquinone-9 and is not accurate for this generic class of compounds, which contains plastoquinones with different side-chain lengths.

a plastoquinone compound structure

Chemical Formula: C53H80O2

Instances:
decylplastoquinone ,
plastoquinone-9

Molecular Weight: 749.21 Daltons

Monoisotopic Molecular Weight: 748.6158318122 Daltons

SMILES: CC(C)=CCCC(=CCCC(C)=CCCC(=CCCC(=CCCC(=CCCC(=CCCC(C)=CCCC(C)=CCC1(=CC(C(=C(C1=O)C)C)=O))C)C)C)C)C

InChI: InChI=1S/C53H80O2/c1-40(2)21-13-22-41(3)23-14-24-42(4)25-15-26-43(5)27-16-28-44(6)29-17-30-45(7)31-18-32-46(8)33-19-34-47(9)35-20-36-48(10)37-38-51-39-52(54)49(11)50(12)53(51)55/h21,23,25,27,29,31,33,35,37,39H,13-20,22,24,26,28,30,32,34,36,38H2,1-12H3/b41-23+,42-25+,43-27+,44-29+,45-31+,46-33+,47-35+,48-37+

Standard Gibbs Free Energy of Change Formation (ΔfG in kcal/mol): 1007.08966 Inferred by computational analysis [Latendresse13]

Reactions known to consume the compound:

hydrogen production VIII , photosynthesis light reactions :
2 a plastoquinol[chloroplast thylakoid membrane] + 4 H+[chloroplast thylakoid lumen] + oxygen[chloroplast thylakoid lumen] ← hν + 2 a plastoquinone[chloroplast thylakoid membrane] + 4 H+[chloroplast stroma] + 2 H2O[chloroplast thylakoid lumen]

trans-lycopene biosynthesis II (plants) :
15,9'-di-cis-phytofluene + a plastoquinone → 9,15,9'-tri-cis-ζ-carotene + a plastoquinol
15-cis-phytoene + a plastoquinone → 15,9'-di-cis-phytofluene + a plastoquinol

(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
7,9,9'-cis-neurosporene + an electron-transfer quinone → prolycopene + an electron-transfer quinol

UMP biosynthesis :
(S)-dihydroorotate + an electron-transfer quinone[inner membrane] → orotate + an electron-transfer quinol[inner membrane]

Not in pathways:
a D-amino acid[in] + an electron-transfer quinone[membrane] + H2O[in] → a 2-oxo carboxylate[in] + ammonium[in] + an electron-transfer quinol[membrane]
D-glucopyranose[out] + an electron-transfer quinone[membrane] + 2 H+[in] → D-glucono-1,5-lactone[out] + an electron-transfer quinol[membrane] + 2 H+[out]
sn-glycerol 3-phosphate[in] + an electron-transfer quinone[membrane] → glycerone phosphate[in] + an electron-transfer quinol[membrane]
an electron-transfer quinone[inner membrane] + NAD(P)H + H+ → an electron-transfer quinol[inner membrane] + NAD(P)+
NADPH + an electron-transfer quinone[inner membrane] + H+ → NADP+ + an electron-transfer quinol[inner membrane]

phenylacetate degradation II (anaerobic) :
phenylacetyl-CoA + 2 a quinone + H2O → 2 a quinol + phenylglyoxylyl-CoA

quinate degradation I :
L-quinate + a quinone → 3-dehydroquinate + a quinol

shikimate degradation I :
shikimate + a quinone → 3-dehydroshikimate + a quinol

thiosulfate oxidation II (via tetrathionate) :
2 thiosulfate + a quinone → tetrathionate + a quinol

Not in pathways:
a cyclic alcohol + a quinonea cyclic ketone + a quinol

Not in pathways:
a cyclic alcohol + a quinonea cyclic ketone + a quinol

Reactions known to produce the compound:

hydrogen production VIII , photosynthesis light reactions :
2 an oxidized plastocyanin[chloroplast thylakoid lumen] + a plastoquinol[chloroplast thylakoid membrane] + 2 H+[chloroplast stroma] → 2 a reduced plastocyanin[chloroplast thylakoid lumen] + a plastoquinone[chloroplast thylakoid membrane] + 4 H+[chloroplast thylakoid lumen]

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:

hydrogen production VIII :
a plastoquinone + NAD(P)H + H+ ↔ a plastoquinol + NAD(P)+

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:
15-cis-phytoene + 2 a plastoquinone = 9,15,9'-tri-cis-ζ-carotene + 2 a plastoquinol

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 Redox half-reactions:
a plastoquinone[membrane] + 2 H+[out] + 2 e-[membrane] → a plastoquinol[membrane] ,
a plastoquinone[membrane] + 2 H+[in] + 2 e-[membrane] → a plastoquinol[membrane] ,
a plastoquinone[membrane] + 4 H+[in] + 2 e-[membrane] → a plastoquinol[membrane] + 2 H+[out] ,
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

Collins81: Collins MD, Jones D (1981). "Distribution of isoprenoid quinone structural types in bacteria and their taxonomic implication." Microbiol Rev 45(2);316-54. PMID: 7022156

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

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


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 Sat Aug 1, 2015, BIOCYC14B.