MetaCyc Compound: L-ascorbate

Systematic Name: L-ascorbate acid

Synonyms: L-ascorbic acid, ascorbate, vitamin C, ascorbic acid

Superclasses: a vitamin

L-ascorbate, also known as vitamin C, fulfils multiple essential roles in both plants and animals. Being a strong reducing agent, it functions as the primary water soluble antioxidant in cells, interacting with reactive oxygen species generated during oxidative stress and protecting cell constituents from oxidative damage [Simpson00]. It also functions as a cofactor for several enzymes, which are involved in many important pathways, including collagen hydroxylation, carnitine biosynthesis, norepinephrine biosynthesis, and hormone and tyrosine metabolism. In plants L-ascorbate is also implicated in defense against pathogens and in control of plant growth and development. A significant proportion of a plant's ascorbate is found in the apoplast (the aqueous solution permeating the cell walls) [Green05].

While most organisms synthesize L-ascorbate, not all do. Examples for organisms that are not able to synthesize L-ascorbate include simians and humans.

Chemical Formula: C6H7O6

Molecular Weight: 175.12 Daltons

Monoisotopic Molecular Weight: 176.0320879894 Daltons

L-ascorbate compound structure

SMILES: C(O)C(O)[CH]1(C([O-])=C(O)C(=O)O1)

InChI: InChI=1S/C6H8O6/c7-1-2(8)5-3(9)4(10)6(11)12-5/h2,5,7-10H,1H2/p-1/t2-,5+/m0/s1


Unification Links: CAS:50-81-7, ChEBI:38290, ChemSpider:102746, HMDB:HMDB00044, IAF1260:33747, KEGG:C00072, KNApSAcK:C00001179, MetaboLights:MTBLC38290, PubChem:54679076

Standard Gibbs Free Energy of Change Formation (ΔfG in kcal/mol): -146.72423Inferred by computational analysis [Latendresse13]

Reactions known to consume the compound:

ascorbate glutathione cycle :
2 L-ascorbate + hydrogen peroxide + 2 H+ → 2 monodehydroascorbate radical + 2 H2O

ascorbate recycling (cytosolic) :
2 L-ascorbate + an oxidized unknown electron acceptor + 2 H+ → 2 monodehydroascorbate radical + an reduced unknown electron acceptor

betaxanthin biosynthesis (via dopaxanthin) :
portulacaxanthin II + L-ascorbate + H+ + oxygen → dopaxanthin + L-dehydro-ascorbate + H2O

catecholamine biosynthesis :
dopamine + L-ascorbate + H+ + oxygen → L-dehydro-ascorbate + (R)-noradrenaline + H2O

ethylene biosynthesis I (plants) :
L-ascorbate + 1-aminocyclopropane-1-carboxylate + H+ + oxygen → ethylene + L-dehydro-ascorbate + hydrogen cyanide + CO2 + 2 H2O

indole glucosinolate breakdown (insect chewing induced) :
indolylmethylisothiocyanate + L-ascorbate → ascorbigen + thiocyanate
indole-3-carbinol + L-ascorbate + H+ → ascorbigen + H2O

L-ascorbate degradation II (bacterial, aerobic) , L-ascorbate degradation III , L-ascorbate degradation V :
2 L-ascorbate + hydrogen peroxide + H+L-ascorbate + L-dehydro-ascorbate + 2 H2O

octopamine biosynthesis :
tyramine + L-ascorbate + oxygen + H+ → octopamine + L-dehydro-ascorbate + H2O

zeaxanthin, antheraxanthin and violaxanthin interconversion :
antheraxanthin + L-ascorbate + H+ → zeaxanthin + L-dehydro-ascorbate + H2O
violaxanthin + L-ascorbate + H+ → antheraxanthin + L-dehydro-ascorbate + H2O

Not in pathways:
L-ascorbate + 2 an oxidized c-type cytochrome → L-dehydro-ascorbate + 2 a reduced c-type cytochrome + H+
L-ascorbate[in] + Fe3+[out] → monodehydroascorbate radical[in] + Fe2+[out]
a [protein] C-terminal glycine + L-ascorbate + oxygen → a [protein] C-terminal hydroxyglycine + L-dehydro-ascorbate + H2O
4 L-ascorbate + oxygen + 4 H+ → 4 monodehydroascorbate radical + 2 H2O

Reactions known to produce the compound:

ascorbate glutathione cycle :
L-dehydro-ascorbate + 2 glutathione → L-ascorbate + glutathione disulfide + H+
2 monodehydroascorbate radical + NADPH + H+ → 2 L-ascorbate + NADP+ + 2 H+
2 monodehydroascorbate radical → L-ascorbate + L-dehydro-ascorbate + H+

ascorbate recycling (cytosolic) :
2 monodehydroascorbate radical + NADH → 2 L-ascorbate + NAD+ + H+
L-dehydro-ascorbate + NADPH → L-ascorbate + NADP+
L-dehydro-ascorbate + 2 glutathione → L-ascorbate + glutathione disulfide + H+
2 monodehydroascorbate radical + NADPH + H+ → 2 L-ascorbate + NADP+ + 2 H+
2 monodehydroascorbate radical → L-ascorbate + L-dehydro-ascorbate + H+

L-ascorbate biosynthesis I (L-galactose pathway) :
L-galactono-1,4-lactone + 2 an oxidized c-type cytochrome → L-ascorbate + 2 a reduced c-type cytochrome + 3 H+

L-ascorbate biosynthesis II (L-gulose pathway) :
L-gulono-1,4-lactone + 2 an oxidized c-type cytochrome → L-ascorbate + 2 a reduced c-type cytochrome + 3 H+

L-ascorbate biosynthesis III :
L-sorbosone 1,4-lactone + an oxidized unknown electron acceptor → L-ascorbate + an reduced unknown electron acceptor + H+

L-ascorbate biosynthesis IV :
L-xylo-hex-3-ulono-1,4-lactone → L-ascorbate + H+

L-ascorbate biosynthesis V :
L-galactono-1,4-lactone + an oxidized unknown electron acceptor → L-ascorbate + an reduced unknown electron acceptor + H+

Not in pathways:
2-phospho-L-ascorbate + H2O → L-ascorbate + phosphate
L-galactono-1,4-lactone + oxygen → L-ascorbate + hydrogen peroxide + H+
L-gulono-1,4-lactone + oxygen → L-ascorbate + hydrogen peroxide + H+

Reactions known to both consume and produce the compound:

L-ascorbate biosynthesis VI (engineered pathway) , L-ascorbate degradation IV :
L-ascorbate + H2O ↔ 2-keto-L-gulonate

In Reactions of unknown directionality:

Not in pathways:
violaxanthin + 2 L-ascorbate + 2 H+ = zeaxanthin + 2 L-dehydro-ascorbate + 2 H2O
L-ascorbate + acetyl phosphate = 2-phospho-L-ascorbate + acetate + H+
L-ascorbate + diphosphate = 2-phospho-L-ascorbate + phosphate + H+
a ferricytochrome b5 + L-ascorbate = a ferrocytochrome b5 + monodehydroascorbate radical
L-ascorbate + ATP = 2-phospho-L-ascorbate + ADP + H+

In Transport reactions:
L-ascorbate[extracellular space] + H+[extracellular space]L-ascorbate[cytosol] + H+[cytosol],
a [PTS enzyme I]-Nπ-phospho-L-histidine + L-ascorbate[out] → L-ascorbate 6-phosphate[in] + a [PTS enzyme I]-L-histidine

In Redox half-reactions:
monodehydroascorbate radical[in] + e-[membrane]L-ascorbate[in]

Enzymes activated by L-ascorbate, sorted by the type of activation, are:

Activator (Allosteric) of: indole-3-acetaldoxime dehydratase [Shukla68] Activator (Non-allosteric) of: pyruvic oxime dioxygenase [Ono96] Activator (Mechanism unknown) of: taurine dioxygenase [Eichhorn97], naringenin 2-oxoglutarate oxygen oxidoreductase [Lee08d], deacetoxycephalosporin C synthase [Dotzlaf89], deacetoxycephalosporin C hydroxylase [Dotzlaf87], deacetoxycephalosporin C synthase [Dotzlaf87, Baldwin87], isopenicillin N synthase [Castro88], tryptophan dioxygenase [Hitchcock88], gibberellin A15,oxoglutarate:oxygen oxidoreductase [Lange94b], desacetoxyvindoline 4-hydroxylase [De90], thioglucoside glucohydrolase [Bernardi03], thioglucoside glucohydrolase [Shikita99], flavone synthase [Britsch90]

Enzymes inhibited by L-ascorbate, sorted by the type of inhibition, are:

Inhibitor (Mechanism unknown) of: 4-hydrobenzaldehyde synthase [Podstolski02], [thyroglobulin]-3,5-diiodotyrosine synthase [Coval67], GDP-D-mannose-3'',5''-epimerase [Wolucka03], GDP-D-mannose:GDP-L-gulose epimerase [Wolucka03], phenolase [Sato67]

This compound has been characterized as a cofactor or prosthetic group of the following enzymes: anditomin synthase, preandiloid B dehydrogenase, 3-methyl-branched 2,3,4-saturated fatty acyl-CoA hydroxylase, γ-butyrobetaine hydroxylase, ε-N-trimethyllysine hydroxylase, 4-hydroxyphenylpyruvate dioxygenase, 4-hydroxyphenylpyruvate dioxygenase

This compound has been characterized as an alternative substrate of the following enzymes: cytochrome bd-I terminal oxidase

Revised 15-Nov-2012 by Caspi R, SRI International


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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
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