Pantothenic acid is a dimethyl derivative of butyric acid linked by a peptide bond to the amino acid β-alanine. Pantothenic acid is optimally active, and activity in humans resides in the dextroisomer. The name pantothenic acid is derived from the Greek for ‘everywhere’, and this reflects its wide distribution in foods of both plant and animal origin. In most food, pantothenic acid is present as coenzyme A, which is hydrolysed in the intestine to allow passive absorption of pantothenic acid. Pantothenic acid is sometimes erroneously designated vitamin B5, although no formal B vitamin numerology is associated with the vitamin. Because it is water soluble pantothenic acid is not stored in tissues. Pantothenic acid deficiency is only present in individuals with severe malnutrition and is characterised by abnormal skin sensations, as well as vomiting, weakness and fatigue. There is no know toxicity for excessively high doses of the vitamin.
Once absorbed pantothenic acid is converted to 4’-phosphopentetheine through addition of a phosphate group from ATP. Subsequently coenzyme A (CoA) is synthesised from 4’-phosphopentetheine, cysteine and ATP. Coenzyme A functions as a coenzyme for a number of reactions that require the transfer of 2-carbon fragments (acetyl groups). In such reactions, the 2-carbon groups bind to the sulfhydryl group of the molecule reversibly. For example, coenzyme A is required for energy metabolism where importantly it allows the formation of acetyl CoA. Acetyl CoA is central to energy metabolism because it condenses with oxaloacetate to allow entry of 2-carbon groups into the citric acid cycle. Malonyl CoA and HMG CoA are required for the synthesis of fatty acids and cholesterol, respectively. Additionally, pantothenic acid in the form of coenzyme A is also required for the acetylation of certain drugs in order to increase water solubility for excretion.