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Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism. [2] Its main function is to deliver the acetyl group to the citric acid cycle (Krebs cycle) to be oxidized for energy production.
The reactions of the cycle are carried out by eight enzymes that completely oxidize acetate (a two carbon molecule), in the form of acetyl-CoA, into two molecules each of carbon dioxide and water. Through catabolism of sugars, fats, and proteins, the two-carbon organic product acetyl-CoA is produced which enters the citric acid cycle.
ATP + Acetate + CoA → AMP + Pyrophosphate + Acetyl-CoA [1] Once acetyl-CoA is formed it can be used in the TCA cycle in aerobic respiration to produce energy and electron carriers. This is an alternate method to starting the cycle, as the more common way is producing acetyl-CoA from pyruvate through the pyruvate dehydrogenase complex.
The enzyme acetyl-CoA hydrolase (EC 3.1.2.1) catalyzes the reaction acetyl-CoA + H 2 O ⇌ {\displaystyle \rightleftharpoons } CoA + acetate This enzyme belongs to the family of hydrolases , specifically those acting on thioester bonds.
The mevalonate pathway of eukaryotes, archaea, and eubacteria all begin the same way. The sole carbon feed stock of the pathway is acetyl-CoA. The first step condenses two acetyl-CoA molecules to yield acetoacetyl-CoA. This is followed by a second condensation to form HMG-CoA (3-hydroxy-3- methyl-glutaryl-CoA). Reduction of HMG-CoA yields (R ...
Chains with an odd-number of carbons are oxidized in the same manner as even-numbered chains, but the final products are propionyl-CoA and acetyl-CoA. Propionyl-CoA is first carboxylated using a bicarbonate ion into a D-stereoisomer of methylmalonyl-CoA. This reaction involves a biotin co-factor, ATP and the enzyme propionyl-CoA carboxylase. [6]
The reaction involving acetyl-CoA and succinate (EC 2.8.3.18) is part of a modified TCA cycle [4] or forms acetate during fermentation. [5] The reaction involving acetoacetate-CoA and succinate ( EC 2.8.3.5 ) degrades the ketone body acetoacetate formed during ketogenesis .
In enzymology, an acetate CoA-transferase (EC 2.8.3.8) is an enzyme that catalyzes the chemical reaction. acyl-CoA + acetate a fatty acid anion + acetyl-CoA. Thus, the two substrates of this enzyme are acyl-CoA and acetate, whereas its two products are long-chain carboxylate anion and acetyl-CoA.