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Coenzyme A (CoA, SHCoA, CoASH) is a coenzyme, notable for its role in the synthesis and oxidation of fatty acids, and the oxidation of pyruvate in the citric acid cycle.All genomes sequenced to date encode enzymes that use coenzyme A as a substrate, and around 4% of cellular enzymes use it (or a thioester) as a substrate.
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.
Pyruvate oxidation is the step that connects glycolysis and the Krebs cycle. [4] In glycolysis, a single glucose molecule (6 carbons) is split into 2 pyruvates (3 carbons each). Because of this, the link reaction occurs twice for each glucose molecule to produce a total of 2 acetyl-CoA molecules, which can then enter the Krebs cycle.
These reactions have different functions in cells. The reaction involving acetyl-CoA and butyrate (EC 2.8.3.8), for example, forms butyrate during fermentation. [3] 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 following reaction is the oxidation of the fatty acid by FAD to afford an α,β-unsaturated fatty acid thioester of coenzyme A: ACADs can be categorized into three distinct groups based on their specificity for short-, medium-, or long-chain fatty acid acyl-CoA substrates.
Dihydrolipoyl transacetylase (or dihydrolipoamide acetyltransferase) is an enzyme component of the multienzyme pyruvate dehydrogenase complex.The pyruvate dehydrogenase complex is responsible for the pyruvate decarboxylation step that links glycolysis to the citric acid cycle.
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)-mevalonate. These first 3 enzymatic steps are called the upper mevalonate pathway. [4]
The Wood–Ljungdahl pathway is a set of biochemical reactions used by some bacteria. It is also known as the reductive acetyl-coenzyme A pathway. [1] This pathway enables these organisms to use hydrogen (H 2) as an electron donor, and carbon dioxide (CO 2) as an electron acceptor and as a building block to generate acetate for biosynthesis.