Coenzyme A (CoA, CoASH, or HSCoA) is a coenzyme notable for its role in the synthesis and oxidization of fatty acids and the oxidation of pyruvate in the citric acid cycle. It is adapted from beta-mercaptoethylamine, panthothenate, and adenosine triphosphate. It is also a parent compound for other transformation products, including but not limited to, phenylglyoxylyl-CoA, tetracosanoyl-CoA, and 6-hydroxyhex-3-enoyl-CoA. Coenzyme A is synthesized in a five-step process from pantothenate and cysteine. In the first step pantothenate (vitamin B5) is phosphorylated to 4'-phosphopantothenate by the enzyme pantothenate kinase (PanK, CoaA, CoaX). In the second step, a cysteine is added to 4'-phosphopantothenate by the enzyme phosphopantothenoylcysteine synthetase (PPC-DC, CoaB) to form 4'-phospho-N-pantothenoylcysteine (PPC). In the third step, PPC is decarboxylated to 4'-phosphopantetheine by phosphopantothenoylcysteine decarboxylase (CoaC). In the fourth step, 4'-phosphopantetheine is adenylylated to form dephospho-CoA by the enzyme phosphopantetheine adenylyl transferase (CoaD). Finally, dephospho-CoA is phosphorylated using ATP to coenzyme A by the enzyme dephosphocoenzyme A kinase (CoaE). 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. CoA assists in transferring fatty acids from the cytoplasm to the 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 proteins and formyltetrahydrofolate dehydrogenase. Acetyl-CoA is an important molecule itself. It is the precursor to HMG CoA which 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. Its main task is conveying the carbon atoms within the acetyl group to the citric acid cycle to be oxidized for energy production (Wikipedia).