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Oxaloacetic acid
Oxaloacetic acid
Chemical name Oxobutanedioic acid
Other names Oxaloacetic acid
Oxalacetic acid
Oxosuccinic acid
Chemical formula C4H4O5
Molecular mass 132.07 g/mol
Melting point 161 °C
Density  ? g/cm3
pKa value 2.22
CAS number [328-42-7]
EINECS number 206-329-8
Thermodynamic data
Standard enthalpy
of formation
-943.21 kJ/mol
Standard enthalpy
of combustion
-1205.58 kJ/mol
Disclaimer and references


Oxaloacetic acid, also known as oxosuccinic acid or oxalacetic acid, is a four-carbon dicarboxylic acid appearing as an intermediate of the citric acid cycle and gluconeogenesis. In vivo, oxaloacetate (the ionised form of oxaloacetic acid) is formed by the oxidation of L-malate, catalysed by malate dehydrogenase, and reacts with Acetyl-CoA to form citrate, catalysed by citrate synthase. It is also formed in the mesophyll of plants by the condensation of CO2 with phosphoenolpyruvate, catalysed by oxaloacetate decarboxylase. It can be formed from pyruvate as 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 pKa value of 13.02. The enzyme fumarase A from E. coli catalyses the conversion between the keto and enol forms.

Oxaloacetic acid is unstable in solution, decomposing to pyruvic acid by decarboxylation over a period of hours (room temperature) or days (0°C). Refrigerator storage of the solid is recommended for long periods.

See alsoEdit

Citric Acid Cycle Metabolic Pathway
Oxaloacetate Malate Fumarate Succinate Succinyl-CoA
Oxaloacetate wpmp S-malate wpmp Fumarate wpmp Succinate wpmp Succinyl-CoA wpmp
Biochem reaction arrow reverse NNYY horiz med Biochem reaction arrow reverse NNYN horiz med Biochem reaction arrow reverse NNYY horiz med Biochem reaction arrow reverse NNYY horiz med
Acetyl co-A wpmp + H2O Biochem reaction arrow special 1 Biochem reaction arrow special 2 NADH + H+ + CO2
Citrate wpmp H2O Cis-Aconitate wpmp H2O Threo-Ds-isocitrate wpmp NAD(P)+ NAD(P)H + H+ Oxalosuccinate wpmp CO2 2-oxoglutarate wpmp
Biochem reaction arrow foward NYNN horiz med Biochem reaction arrow foward YNNN horiz med Biochem reaction arrow foward YYNN horiz med Biochem reaction arrow foward NYNN horiz med
Citrate cis-Aconitate Isocitrate Oxalosuccinate α-Ketoglutarate
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