El ácido oxaloacético (también conocido como ácido oxalacético o OAA ) es un compuesto orgánico cristalino con la fórmula química HO 2 CC (O) CH 2 CO 2 H. El ácido oxaloacético, en la forma de su oxalacetato de base conjugada , es un intermedio metabólico en muchos procesos que ocurren en animales. Participa en la gluconeogénesis , el ciclo de la urea , el ciclo del glioxilato , amino síntesis de ácidos , síntesis de ácidos grasos y el ciclo del ácido cítrico . [1]
Nombres | |
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Nombre IUPAC preferido Ácido oxobutanodioico | |
Otros nombres Ácido oxalacético Ácido oxalacético Ácido 2-oxosuccínico Ácido cetosuccínico | |
Identificadores | |
Modelo 3D ( JSmol ) | |
CHEBI | |
ChemSpider | |
Tarjeta de información ECHA | 100.005.755 |
Número CE |
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PubChem CID | |
UNII | |
Tablero CompTox ( EPA ) | |
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Propiedades | |
C 4 H 4 O 5 | |
Masa molar | 132,07 g / mol |
Densidad | 0,18 g / cm 3 |
Punto de fusion | 161 ° C (322 ° F; 434 K) |
Termoquímica | |
-943,21 kJ / mol | |
-1205,58 kJ / mol | |
Salvo que se indique lo contrario, los datos se proporcionan para materiales en su estado estándar (a 25 ° C [77 ° F], 100 kPa). | |
verificar ( ¿qué es ?) | |
Referencias de Infobox | |
Propiedades
El ácido oxaloacético sufre sucesivas desprotonaciones para dar al dianión:
- HO 2 CC (O) CH 2 CO 2 H ⇌ - O 2 CC (O) CH 2 CO 2 H + H + , pK a = 2.22
- - O 2 CC (O) CH 2 CO 2 H ⇌ - O 2 CC (O) CH 2 CO 2 - + H + , pK a = 3.89
A pH alto, el protón enolizable se ioniza:
- - O 2 CC (O) CH 2 CO 2 - ⇌ - O 2 CC (O - ) CHCO 2 - + H + , pK a = 13.03
Las formas enol del ácido oxaloacético son particularmente estables, tanto que los dos tautómeros tienen diferentes puntos de fusión (152 ° C para la isoforma cis y 184 ° C para la isoforma trans ). Esta reacción es catalizada por la enzima oxalacetato tautomerasa . El trans -enol-oxalacetato también aparece cuando el tartrato es el sustrato de la fumarasa . [2]
Biosíntesis
El oxaloacetato se forma de varias formas en la naturaleza. Una ruta principal es sobre la oxidación de L -malato , catalizada por la malato deshidrogenasa , en el ciclo del ácido cítrico. El malato también se oxida por la succinato deshidrogenasa en una reacción lenta, siendo el producto inicial enol-oxalacetato. [3]
También surge de la condensación de piruvato con ácido carbónico, impulsada por la hidrólisis de ATP :
- CH 3 C (O) CO 2 - + HCO 3 - + ATP → - O 2 CCH 2 C (O) CO 2 - + ADP + Pi
Ocurriendo en el mesófilo de las plantas, este proceso procede a través del fosfoenolpiruvato , catalizado por la fosfoenolpiruvato carboxilasa .
El oxalacetato también puede surgir de la trans- o demolición del ácido aspártico .
Funciones bioquímicas
Oxaloacetate is an intermediate of the citric acid cycle, where it reacts with acetyl-CoA to form citrate, catalyzed by citrate synthase. It is also involved in gluconeogenesis, the urea cycle, the glyoxylate cycle, amino acid synthesis, and fatty acid synthesis. Oxaloacetate is also a potent inhibitor of complex II.
Gluconeogenesis
Gluconeogenesis[1] is a metabolic pathway consisting of a series of eleven enzyme-catalyzed reactions, resulting in the generation of glucose from non-carbohydrates substrates. The beginning of this process takes place in the mitochondrial matrix, where pyruvate molecules are found. A pyruvate molecule is carboxylated by a pyruvate carboxylase enzyme, activated by a molecule each of ATP and water. This reaction results in the formation of oxaloacetate. NADH reduces oxaloacetate to malate. This transformation is needed to transport the molecule out of the mitochondria. Once in the cytosol, malate is oxidized to oxaloacetate again using NAD+. Then oxaloacetate remains in the cytosol, where the rest of reactions will take place. Oxaloacetate is later decarboxylated and phosphorylated by phosphoenolpyruvate carboxykinase and becomes 2-phosphoenolpyruvate using guanosine triphosphate (GTP) as phosphate source. Glucose is obtained after further downstream processing.
Urea cycle
The urea cycle is a metabolic pathway that results in the formation of urea using one ammonium molecule from degraded amino acids, another ammonium group from aspartate and one bicarbonate molecule.[1] This route commonly occurs in hepatocytes. The reactions related to the urea cycle produce NADH, and NADH can be produced in two different ways. One of these uses oxaloacetate. In the cytosol there are fumarate molecules. Fumarate can be transformed into malate by the actions of the enzyme fumarase. Malate is acted on by malate dehydrogenase to become oxaloacetate, producing a molecule of NADH. After that, oxaloacetate will be recycled to aspartate, as transaminases prefer these keto acids over the others. This recycling maintains the flow of nitrogen into the cell.
Glyoxylate cycle
The glyoxylate cycle is a variant of the citric acid cycle.[4] It is an anabolic pathway occurring in plants and bacteria utilizing the enzymes isocitrate lyase and malate 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 the glyoxylate cycle because its loop of the cycle incorporates two molecules of acetyl-CoA.
Fatty acid synthesis
In previous stages acetyl-CoA is transferred from the mitochondria to the cytoplasm where fatty 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 cytoplasmatic 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:
- HCO 3– + ATP + acetyl-CoA → ADP + P i + malonyl-CoA
Amino acid synthesis
Six essential amino acids and three nonessential are synthesized from oxaloacetate and pyruvate.[6] Aspartate and alanine are formed from oxaloacetate and pyruvate, respectively, by transamination from glutamate. Asparagine, methionine, lysine and threonine are synthesized by aspartate, therefore given importance to oxaloacetate as without it, no aspartate would be formed and the following other amino acids would neither be produced.
Oxalate biosynthesis
Oxaloacetate produces oxalate by hydrolysis.[7]
- oxaloacetate + H 2O ⇌ oxalate + acetate
This process is catalyzed by the enzyme oxaloacetase. This enzyme is seen in plants, but is not known in the animal kingdom. [8]
Mapa de ruta interactivo
Click on genes, proteins and metabolites below to link to respective articles.[§ 1]
| Click on genes, proteins and metabolites below to link to respective articles. [§ 1]
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Ver también
- Dioxosuccinic acid
- Glycolysis
- Oxidative phosphorylation
- Citric acid cycle
Referencias
- ^ a b c d Nelson, David L.; Cox, Michael M. (2005). Principles of Biochemistry (4th ed.). New York: W. H. Freeman. ISBN 0-7167-4339-6.
- ^ van Vugt-Lussenburg, BMA; van der Weel, L; Hagen, WR; Hagedoorn, P-L (February 26, 2021), Biochemical Similarities and Differences between the Catalytic [4Fe-4S] Cluster Containing Fumarases FumA and FumB from Escherichia coli (published February 6, 2013), doi:10.1371/journal.pone.0055549
- ^ M.V. Panchenko; A.D. Vinogradov (1991). "Direct demonstration of enol-oxaloacetate as an immediate product of malate oxidation by the mammalian succinate dehydrogenase". FEBS Letters. 286 (1–2): 76–78. doi:10.1016/0014-5793(91)80944-X.
- ^ "Welcome to The Chemistry Place". www.pearsonhighered.com. Retrieved 5 April 2018.
- ^ "fatty acids synthesis". http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb2/part1/fasynthesis.htm. External link in
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(help) - ^ "http://faculty.ksu.edu.sa/69436/Documents/lecture-15-aa_from_oxaloacetate_and_pyruvate.pptx". Archived from the original on 2013-10-21. Retrieved 2013-10-21. External link in
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(help) - ^ Gadd, Geoffrey M. "Fungal production of citric and oxalic acid: importance in metal speciation, physiology and biogeochemical processes" Advances in Microbial Physiology (1999), 41, 47-92.
- ^ Xu, Hua-Wei. "Oxalate accumulation and regulations is independent of glycolate oxidase in rice leaves" Journal of Experimental Botany, Vol 57, No. 9 pp. 1899-1908, 2006