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| Names | |
|---|---|
| Preferred IUPAC name 2-Oxobutanedioic acid | |
| Other names Oxaloacetic acid Oxalacetic acid 2-Oxosuccinic acid Ketosuccinic acid | |
| Identifiers | |
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3D model (JSmol) | |
| ChEBI | |
| ChemSpider |
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| ECHA InfoCard | 100.005.755 |
| EC Number |
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| KEGG |
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| UNII | |
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| Properties | |
| C4H4O5 | |
| Molar mass | 132.07 g/mol |
| Density | 1.6 g/cm3 |
| Melting point | 161 °C (322 °F; 434 K) |
| Thermochemistry | |
Std enthalpy of formation(ΔfH⦵298) | −943.21 kJ/mol |
Std enthalpy of combustion(ΔcH⦵298) | −1205.58 kJ/mol |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Oxaloacetic acid (also known asoxalacetic acid orOAA) is a crystallineorganic compound with thechemical formula HO2CC(O)CH2CO2H. Oxaloacetic acid, in the form of itsconjugate baseoxaloacetate, is ametabolic intermediate in many processes that occur in animals. It takes part ingluconeogenesis, theurea cycle, theglyoxylate cycle,amino acid synthesis,fatty acid synthesis and thecitric acid cycle.[1]
Oxaloacetic acid undergoes successivedeprotonations to give thedianion:
At highpH, the enolizable proton is ionized:
Theenol forms of oxaloacetic acid are particularly stable.Keto-enol tautomerization is catalyzed by the enzymeoxaloacetate tautomerase.trans-Enol-oxaloacetate also appears whentartrate is the substrate forfumarase.[2]
Oxaloacetate forms in several ways in nature. A principal route is uponoxidation ofL-malate, catalyzed bymalate dehydrogenase, in the citric acid cycle. Malate is also oxidized bysuccinate dehydrogenase in a slow reaction with the initial product being enol-oxaloacetate.[3]
It also arises from the condensation ofpyruvate with carbonic acid, driven by the hydrolysis ofATP:
Occurring in themesophyll of plants, this process proceeds viaphosphoenolpyruvate, catalysed byphosphoenolpyruvate carboxylase.
Oxaloacetate can also arise fromtrans- or de- amination ofaspartic acid.
Oxaloacetate is an intermediate of thecitric acid cycle, where it reacts withacetyl-CoA to formcitrate, catalyzed bycitrate synthase. It is also involved ingluconeogenesis, theurea cycle, theglyoxylate cycle,amino acid synthesis, andfatty acid synthesis. Oxaloacetate is also a potent inhibitor ofcomplex II.
Gluconeogenesis[1] is a metabolic pathway consisting of a series of eleven enzyme-catalyzed reactions, resulting in the generation ofglucose from non-carbohydrates substrates. The beginning of this process takes place in themitochondrial matrix, wherepyruvate molecules are found. A pyruvate molecule is carboxylated by apyruvate carboxylase enzyme, activated by a molecule each ofATP and water. This reaction results in the formation of oxaloacetate.NADH reduces oxaloacetate tomalate. This transformation is needed to transport the molecule out of themitochondria. Once in thecytosol, malate is oxidized to oxaloacetate again using NAD+. Then oxaloacetate remains in the cytosol, where the rest of reactions will take place. Oxaloacetate is laterdecarboxylated andphosphorylated byphosphoenolpyruvate carboxykinase and becomes2-phosphoenolpyruvate usingguanosine triphosphate (GTP) as phosphate source. Glucose is obtained after further downstream processing.
Theurea cycle is a metabolic pathway that results in the formation ofurea using one ammonium molecule from degraded amino acids, another ammonium group from aspartate and one bicarbonate molecule.[1] This route commonly occurs inhepatocytes. The reactions related to the urea cycle produceNADH, and NADH can be produced in two different ways. One of these usesoxaloacetate. In the cytosol there arefumarate molecules. Fumarate can be transformed intomalate by the actions of the enzymefumarase. Malate is acted on by malate dehydrogenase to become oxaloacetate, producing a molecule of NADH. After that, oxaloacetate will be recycled toaspartate, astransaminases prefer theseketo acids over the others. This recycling maintains the flow ofnitrogen into the cell.
Theglyoxylate cycle is a variant of the citric acid cycle.[4] It is ananabolic pathway occurring inplants andbacteria utilizing the enzymesisocitrate lyase andmalate synthase. Some intermediate steps of the cycle are slightly different from the citric acid cycle; nevertheless oxaloacetate has the same function in both processes.[1] This means that oxaloacetate in this cycle also acts as the primary reactant and final product. In fact the oxaloacetate is a net product of theglyoxylate cycle because its loop of the cycle incorporates two molecules of acetyl-CoA.
In previous stages acetyl-CoA is transferred from the mitochondria to the cytoplasm wherefatty acid synthase resides. The acetyl-CoA is transported as a citrate, which has been previously formed in the mitochondrial matrix from acetyl-CoA and oxaloacetate. This reaction usually initiates the citric acid cycle, but when there is no need of energy it is transported to the cytoplasm where it is broken down to cytoplasmic acetyl-CoA and oxaloacetate.
Another part of the cycle requires NADPH for the synthesis of fatty acids.[5] Part of this reducing power is generated when the cytosolic oxaloacetate is returned to the mitochondria as long as the internal mitochondrial layer is non-permeable for oxaloacetate. Firstly the oxaloacetate is reduced to malate using NADH. Then the malate is decarboxylated to pyruvate. Now this pyruvate can easily enter the mitochondria, where it is carboxylated again to oxaloacetate by pyruvate carboxylase. In this way, the transfer of acetyl-CoA that is from the mitochondria into the cytoplasm produces a molecule of NADH. The overall reaction, which is spontaneous, may be summarized as:
Six essential amino acids and three nonessential are synthesized fromoxaloacetate and pyruvate.[6] Aspartate and alanine are formed from oxaloacetate and pyruvate, respectively, by transamination fromglutamate. Asparagine is synthesized by amidation of aspartate, with glutamine donating the NH4.These are nonessential amino acids, and their simple biosynthetic pathways occur in all organisms. Methionine, threonine, lysine, isoleucine, valine, and leucine are essential amino acids in humans and most vertebrates. Their biosynthetic pathways in bacteria are complex and interconnected.
Oxaloacetate produces oxalate by hydrolysis.[7]
This process is catalyzed by theenzymeoxaloacetase. This enzyme is seen in plants, but is not known in the animal kingdom.[8]
| Click on genes, proteins and metabolites below to link to respective articles.[§ 1] [[File:  [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] Glycolysis and Gluconeogenesisedit
| Click on genes, proteins and metabolites below to link to respective articles.[§ 1] [[File:  [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] [[]] TCACycle_WP78edit
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