Oxaloacetic acid

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Oxaloacetic acid
IUPAC name	Oxobutanedioic acid
Other names	Oxaloacetic acid Oxalacetic acid Oxosuccinic acid
Identifiers
CAS number	[328-42-7]
EINECS number	206-329-8
SMILES	OC(C(CC(O)=O)=O)=O
Properties
Molecular formula	C4H4O5
Molar mass	132.07 g/mol
Density	? g/cm3
Melting point	161 °C
Thermochemistry
Std enthalpy of formation ΔfHo298	-943.21 kJ/mol
Std enthalpy of combustion ΔcHo298	-1205.58 kJ/mol
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Oxaloacetic acid is an organic compound with the chemical formula HO₂CC(O)CH₂CO₂H. It also has other names (see Table) and its conjugate base is called "oxaloacetate." This four-carbon dicarboxylic acid is a protonated variant of oxaloacetate, which is an intermediate of the citric acid cycle and gluconeogenesis. Oxaloacetate forms upon oxidation of L-malate, catalysed by malate dehydrogenase, and reacts with Acetyl-CoA to form citrate, catalysed by citrate synthase. It also forms in the mesophyll of plants by the condensation of CO₂ with phosphoenolpyruvate, catalysed by PEP Carboxykinase. It can arise from pyruvate via an anaplerotic reaction.

The enol forms of oxaloacetic acid are particularly stable, so much so that the two isomers have different melting points (152 °C cis, 184 °C trans). The enol proton has a pK_a value of 13.02. The enzyme fumarase A from E. coli catalyses the conversion between the keto and enol forms.

Oxaloacetate is unstable in solution, decomposing to pyruvate by decarboxylation over a period of hours (room temperature) or days (0 °C). Refrigerated storage of the solid is therefore recommended.

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v • d • e Citric Acid Cycle Metabolic Pathway
Oxaloacetate Malate Fumarate Succinate Succinyl-CoA Acetyl-CoA NADH + H+ NAD+ H2O FADH2 FAD CoA + ATP(GTP) Pi + ADP(GDP) + H2O NADH + H+ + CO2 CoA NAD+ H2O H2O NAD(P)+ NAD(P)H + H+ CO2 Citrate cis-Aconitate Isocitrate Oxalosuccinate α-Ketoglutarate