Acetyl coenzyme A.
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| Surname | Acetyl coenzyme A. | ||||||||||||||||||
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| Molecular formula | C 23 H 38 N 7 O 17 P 3 S | ||||||||||||||||||
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| Molar mass | 809.57 g mol −1 | ||||||||||||||||||
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| As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . | |||||||||||||||||||
Acetyl-Coenzyme A (acetyl-CoA for short) is an "activated" acetic acid residue (CH 3 CO - ). This is bound to the SH group of the cysteamine part of coenzyme A. It is derived from the esterification of the SH group of coenzyme A with acetic acid .
Occurrence and biological importance
Due to the high group transfer potential of the thioester group , acetyl-coenzyme A plays a key role in numerous metabolic reactions in which C 2 fragments (acetate units) are converted.
In humans, acetyl-CoA is the most important intermediate product in the cell metabolism of the three main nutrients, carbohydrates , lipids and amino acids .
Acetyl-CoA is produced in the organism during several metabolic processes :
- On the one hand, it is formed by the oxidative decarboxylation of pyruvate (which in turn is the end product of glycolysis ), but also by the breakdown of amino acids (such as L -alanine ). The oxidative decarboxylation of pyruvate takes place in the mitochondrion . There the pyruvate dehydrogenase enzyme complex catalyzes the splitting off of carbon dioxide CO 2 (the carboxy group is split off, hence “decarboxylation”) and at the same time the linkage of the remaining acetyl residue with the SH group of coenzyme A. The originally central carbon atom of the pyruvate is oxidized (hence "oxidative").
- In addition, acetyl-CoA is formed during the breakdown of fatty acids in the course of β-oxidation . Here, two carbon atoms in the form of acetyl-CoA are split off from the fatty acid one after the other. So z. B. in the degradation of palmitic acid with 16 carbon atoms in the context of β-oxidation eight molecules of acetyl-CoA. This process also takes place in the mitochondrial matrix.
- In the assimilatory metabolism of many anaerobes , it also occurs as a product of the reductive acetyl-CoA pathway and the reductive citric acid cycle .
The acetyl-CoA formed can be completely broken down in the mitochondrion by the citric acid cycle and respiratory chain to CO 2 and H 2 O or it can be used again for the synthesis of high-energy compounds such as triglycerides , ketone bodies or cholesterol . Some of these anabolic processes take place in the cytosol (e.g. fatty acid synthesis ), but the acetyl-CoA cannot easily leave the mitochondrion and the transport routes for longer-chain carboxylic acids (see below) are also blocked. For the transport of acetyl-CoA from the mitochondrion into the cytosol there is therefore a special transport system, the so-called citrate shuttle .
Individual evidence
- ↑ This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.
- ↑ a b Spektrum.de: Acetyl-Coenzyme A - Lexicon of Biology , accessed on April 18, 2017
- ↑ Florian Horn: Human biochemistry, the textbook for medical studies . Georg Thieme Verlag, 2009, ISBN 978-3-13-130884-9 , p. 200 ( limited preview in Google Book Search).