Acetyl-CoA 190273 225337969 2008-07-13T04:24:36Z Bform 4183934 /* Other reactions */ added info regarding acetylation as post translational modification. And removed redundacy relating to hmgcoa/cholesterol {{Chembox new | ImageFile = Acetyl-CoA-2D.svg | ImageSize = 350px | ImageFile2 = Acetyl-CoA-3D-balls.png | IUPACName = | OtherNames = | Section1 = {{Chembox Identifiers | CASNo = 72-89-9 | PubChem = 181 | SMILES = O=C(NCCSC(=O)C)CCNC<br>(=O)[C@H](O)C(C)(C) COP(=O)(O)OP(=O)<br>(O)OC[C@H]1O[C@H] ([C@H](O)[C@@H]1OP(=O)<br>(O)O)n1cnc2c(N)ncnc12 | MeSHName = Acetyl+Coenzyme+A }} | Section2 = {{Chembox Properties | Formula = C<sub>23</sub>H<sub>38</sub>N<sub>7</sub>O<sub>17</sub>P<sub>3</sub>S | MolarMass = 809.572 | Appearance = | Density = | MeltingPt = | BoilingPt = }} | Section3 = {{Chembox Hazards | Solubility = | MainHazards = | FlashPt = | Autoignition = }} }} '''Acetyl-CoA''' is an important molecule in metabolism, used in many biochemical reactions. Its main use is to convey the [[carbon]] [[atom]]s within the [[acetyl]] group to the [[citric acid cycle]] to be [[oxidation|oxidized]] for energy production. In chemical structure, acetyl-CoA is the [[thioester]] between [[coenzyme A]] (a [[thiol]]) and [[acetic acid]] (an [[acyl]] group carrier). Acetyl-CoA is produced during the second step of aerobic [[cellular respiration]], [[pyruvate decarboxylation]], which occurs in the [[Matrix (biology)|matrix]] of the [[mitochondria]]. Acetyl-CoA then enters the citric acid cycle. Acetyl-CoA is also an important component in the biogenic synthesis of the neurotransmitter [[acetylcholine]]. [[Choline]], in combination with Acetyl-CoA, is catalyzed by the enzyme [[choline acetyltransferase]] to produce acetylcholine and a [[coenzyme a]] byproduct. ==Functions== ===Pyruvate dehydrogenase and pyruvate formate lyase reactions=== The oxidative conversion of [[pyruvate]] into acetyl-CoA is referred to as the '''pyruvate dehydrogenase reaction'''. It is catalyzed by the [[pyruvate dehydrogenase complex]]. Other conversions between pyruvate and acetyl-CoA are possible. For example, [[pyruvate formate lyase]] disproportionates pyruvate into acetyl-CoA and [[formic acid]]. The pyruvate formate lyase reaction does not involve any net oxidation or reduction. ===Fatty acid metabolism=== In animals, acetyl-CoA is very central to the balance between [[carbohydrate metabolism]] and [[fat]] metabolism (see [[fatty acid synthesis]]). In normal circumstances, acetyl-CoA from fatty acid metabolism feeds into the [[citric acid cycle]], contributing to the cell's energy supply. In the [[liver]], when levels of circulating fatty acids are high, the production of acetyl-CoA from fat breakdown exceeds the cellular energy requirements. To make use of the energy available from the excess acetyl-CoA, [[ketone bodies]] are produced which can then circulate in the blood. In some circumstances, this can lead to the presence of ketone bodies in the [[blood]], a condition called [[ketosis]]. Benign dietary ketosis can safely occur in people following [[low-carbohydrate diet]]s, which cause fats to be metabolised as a major source of energy. This is different from [[ketosis]] brought on as a result of starvation and [[ketoacidosis]], a dangerous condition that can affect [[diabetics]]. In plants, de novo fatty acid synthesis occurs in the plastids. Many seeds accumulate large reservoirs of seed oils to support [[germination]] and early growth of the seedling before it is a net photosynthetic organism. Fatty acids are incorporated into membrane lipids, the major component of most membranes. ===Other reactions=== * Two acetyl-CoA can be [[Condensation reaction|condensed]] to create [[acetoacetyl-CoA]], the first step in the HMG-CoA/ [[mevalonic acid pathway]] leading to synthesis of [[isoprenoid]]s. In animals HMG-CoA is a vital precursor to [[cholesterol]] and [[Ketone bodies|ketone]] synthesis. * Acetyl-CoA is also the source of the acetyl group incorporated onto certain lysine residues of histone and non-histone proteins in the post-translational modification [[acetylation]], a reaction catalyzed by [[acetyltransferases]]. * In plants and animals, cytosolic acetyl-CoA is synthesized by [[ATP citrate lyase]] [http://www.plantphysiol.org/cgi/content/full/130/2/740]. When glucose is abundant in the blood of animals, it is converted via [[glycolysis]] in the [[cytosol]] to [[pyruvate]], and thence to acetyl-CoA in the mitochondrion. The excess of [[acetyl-CoA]] results in production of excess [[citrate]], which is exported into the cytosol to give rise to cytosolic acetyl-CoA. * Acetyl-CoA can be [[carboxylated]] in the cytosol by [[acetyl-CoA carboxylase]], giving rise to [[malonyl-CoA]], a substrate required for synthesis of flavonoids and related polyketides, for elongation of fatty acids to produce waxes, [[cuticle]], and seed oils in members of the [[Brassica]] family, and for malonation of proteins and other phytochemicals [http://www.plantcell.org/cgi/content/full/17/1/182]. * In plants, these include [[sesquiterpene]]s, [[brassinosteroid]]s (hormones), and membrane [[sterol]]s. == See also == * [[Citric acid cycle]] * [[HMG-CoA reductase pathway]] * [[Fatty acid metabolism]] * [[Acyl CoA]] * [[Acetyl Co-A synthetase]] * [[Malonyl-CoA decarboxylase]] ==External links== * {{MeshName|Acetyl+Coenzyme+A}} {{Cholesterol metabolism intermediates}} [[Category:Metabolism]] [[Category:Thioesters]] [[Category:Coenzymes]] [[cs:Acetyl-CoA]] [[de:Coenzym A#Acetyl-CoA]] [[es:Acetil-CoA]] [[eo:Acetila Koenzimo A]] [[fr:Acétyl-coenzyme A]] [[it:Acetil-coenzima A]] [[he:אצטיל קואנזים A]] [[lb:HSCoA]] [[hu:Acetil-koenzim A]] [[nl:Acetyl-CoA]] [[ja:アセチルCoA]] [[pt:Acetilcoenzima A]] [[fi:Asetyylikoentsyymi-A]] [[sv:Acetyl-CoA]] [[tr:Asetil CoA]] [[zh:乙酰辅酶A]]