Coenzyme A

Coenzyme A (CoA, CoASH, or HSCoA) 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 sequenced genomes encode enzymes that use coenzyme A as a substrate, and around 4% of cellular enzymes use it (or a thioester, such as acetyl-CoA) as a substrate. It is adapted from cysteamine, pantothenate, and adenosine triphosphate.

Biosynthesis
Coenzyme A is synthesized in a five-step process from pantothenate and cysteine:
 * 1) Pantothenate (vitamin B5) is phosphorylated to 4'-phosphopantothenate by the enzyme pantothenate kinase (PanK; CoaA; CoaX)
 * 2) A cysteine is added to 4'-phosphopantothenate by the enzyme phosphopantothenoylcysteine synthetase (PPC-DC; CoaB) to form 4'-phospho-N-pantothenoylcysteine (PPC)
 * 3) PPC is decarboxylated to 4'-phosphopantetheine by phosphopantothenoylcysteine decarboxylase (CoaC)
 * 4) 4'-phosphopantetheine is adenylylated to form dephospho-CoA by the enzyme phosphopantetheine adenylyl transferase (CoaD)
 * 5) Finally, dephospho-CoA is phosphorylated using ATP to coenzyme A by the enzyme dephosphocoenzyme A kinase (CoaE).

Function
Since coenzyme A is, in chemical terms, a thiol, it can react with carboxylic acids to form thioesters, thus functioning as an acyl group carrier. It assists in transferring fatty acids from the cytoplasm to mitochondria. A molecule of coenzyme A carrying an acetyl group is also referred to as acetyl-CoA. When it is not attached to an acyl group, it is usually referred to as 'CoASH' or 'HSCoA'.

Coenzyme A is also the source of the phosphopantetheine group that is added as a prosthetic group to proteins such as acyl carrier protein and formyltetrahydrofolate dehydrogenase.

List of coenzyme A activated acyl groups

 * Acetyl-CoA
 * Propionyl-CoA
 * Acetoacetyl-CoA
 * Coumaroyl-CoA (used in flavonoid and stilbenoid biosynthesis)
 * Acyl derived from dicarboxylic acids
 * Malonyl-CoA
 * Succinyl-CoA (used in heme biosynthesis)
 * Hydroxymethylglutaryl-CoA (used in isoprenoid biosynthesis)
 * Pimelyl-CoA (used in biotin biosynthesis)
 * fatty acyl-CoA (activated form of all fatty acids; only the CoA esters are substrates for important reactions such as mono-, di-, and triacylglycerol synthesis, carnitine palmitoyl transferase, and cholesterol esterification)
 * Benzoyl CoA
 * Phenylacetyl CoA
 * Butyryl CoA