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Oxaloacetic acid (also known as oxalacetic acid or OAA) is a crystalline organic compound with the chemical formula HO 2 CC(O)CH 2 CO 2 H. Oxaloacetic acid, in the form of its conjugate base oxaloacetate, is a metabolic intermediate in many processes that occur in animals.
The reaction it catalyzes is: pyruvate + HCO − 3 + ATP → oxaloacetate + ADP + P. It is an important anaplerotic reaction that creates oxaloacetate from pyruvate. PC contains a biotin prosthetic group [1] and is typically localized to the mitochondria in eukaryotes with exceptions to some fungal species such as Aspergillus nidulans which have a cytosolic PC.
Phosphoenolpyruvate carboxylase (also known as PEP carboxylase, PEPCase, or PEPC; EC 4.1.1.31, PDB ID: 3ZGE) is an enzyme in the family of carboxy-lyases found in plants and some bacteria that catalyzes the addition of bicarbonate (HCO 3 −) to phosphoenolpyruvate (PEP) to form the four-carbon compound oxaloacetate and inorganic phosphate: [1]
Malate, in the mitochondrial matrix, can be used to make pyruvate (catalyzed by malic enzyme) or oxaloacetic acid, both of which can enter the citric acid cycle. Glutamine can also be used to produce oxaloacetate during anaplerotic reactions in various cell types through "glutaminolysis", which is also seen in many c-Myc transformed cells. [3]
There it is cleaved by ATP citrate lyase into acetyl-CoA and oxaloacetate. The oxaloacetate can be used for gluconeogenesis (in the liver), or it can be returned into mitochondrion as malate. [8] The cytosolic acetyl-CoA is carboxylated by acetyl-CoA carboxylase into malonyl-CoA, the first committed step in the synthesis of fatty acids. [8] [9]
The ketones are released by the liver into the blood. All cells with mitochondria can take up ketones from the blood and reconvert them into acetyl-CoA, which can then be used as fuel in their citric acid cycles, as no other tissue can divert its oxaloacetate into the gluconeogenic pathway in the way that this can occur in the liver.
Ketone bodies are water-soluble molecules or compounds that contain the ketone groups produced from fatty acids by the liver (ketogenesis). [1] [2] Ketone bodies are readily transported into tissues outside the liver, where they are converted into acetyl-CoA (acetyl-Coenzyme A) – which then enters the citric acid cycle (Krebs cycle) and is oxidized for energy.
In enzymology, an oxaloacetase (EC 3.7.1.1) is an enzyme that catalyzes the chemical reaction: [1]. oxaloacetate + H 2 O oxalate + acetate. Thus, the two substrates of this enzyme are oxaloacetate and H 2 O, whereas its two products are oxalate and acetate.