Acetyl-CoA is an important molecule in metabolism, used in many biochemical reactions. Its main use is to convey the carbon atoms within the acetyl group to the citric acid cycle to be oxidized for energy production. Chemically it is the thioester between coenzyme A (an acyl group carrier) and acetic acid. Acetyl-CoA is produced during the second step of aerobic cellular respiration, pyruvate decarboxylation, which occurs in the matrix of the mitochondria. Acetyl-CoA then enters the Krebs Cycle.
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references
The enzyme consists of 60 subunits:
The reaction of this complex follows three steps:
In animals, acetyl-CoA is very central to the balance between carbohydrate metabolism and fat metabolism. Normally, 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 an excess of ketone bodies in the blood, a condition known as ketoacidosis. This can occur in diabetes, starvation or in people following low-carbohydrate diets, all of which can cause fats to be metabolised as a major source of energy.
In plants, de novo fatty acid synthesis occurs in the plastids. Many seeds accumulate large resevoirs 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.
It is the precursor to HMG-CoA, which, in animals, is a vital component in cholesterol and ketone synthesis. Furthermore, it contributes an acetyl group to choline to produce acetylcholine, in a reaction catalysed by choline acetyltransferase.
In plants and animals, cytosolic acetyl-CoA is synthesized by ATP citrate lyase . 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 flavonones and related polyketides, for elongation of fatty acids to produce waxes, cuticle, seed oils in members of the Brassica family, and for malonation of proteins and other phytochemicals .
Two acetyl-CoA can be condensed to create acetoacetyl-CoA, the first step in the HMG-CoA/ mevalonic acid pathway leading to synthesis of isoprenoids. In plants these include sesquiterpenes, brassinosteroids (hormones), and membrane sterols.
The content of this section is licensed under the GNU Free Documentation License (local copy). It uses material from the Wikipedia article "Acetyl-CoA" modified March 11, 2007 with previous authors listed in its history.