描述
Panthothenate (vitamin B5) is the precursor of coenzyme A and is the prosthetic group of acyl carrier protein (ACP). Its name is derived from the Greek pantothen meaning "from everywhere" and small quantities of pantothenic acid are found in nearly every foodstuff. Coenzyme A (CoA) may act as an acyl group carrier to form acetyl-CoA and other related compounds and is used as a way to transport carbon atoms within the cell. CoA is important in energy metabolism for pyruvate to enter TCA cycle as acetyl-CoA, and for α-ketoglutarate to be transformed to succinyl-CoA in the cycle. CoA is also important in the biosynthesis of many important compounds such as fatty acids, cholesterol, and acetylcholine. About 85% of dietary pantothenic acid is as CoA or phosphopentetheine. In the intestinal lumen, these undergo hydrolysis to phosphopantetheine, then pantetheine. Intestinal mucosal cells have high pantetheinase activity and rapidly hydrolyze pantetheine to yield free pantothenic acid. Coenzyme A is synthesized in a five-step process from pantothenate. First, antothenate (Vitamin B5) is phosphorylated to 4'-phosphopantothenate by the enzyme pantothenate kinase, next a cysteine is added to 4'-phosphopantothenate by the enzyme phosphopantothenoylcysteine synthetase to form 4'-phospho-N-pantothenoylcysteine (PPC). In the next step, PPC is decarboxylated to 4'-phosphopantetheine by phosphopantothenoylcysteine decarboxylase. In the fourth step, 4'-phosphopantetheine is adenylylated to form dephospho-CoA by the enzyme phosphopantetheine adenylyl transferase. Finally, dephospho-CoA is phosphorylated using ATP to coenzyme A by the enzyme dephosphocoenzyme A kinase. CoA undergoes dephosphorylation, catalyzed by lysosomal acid phosphatasae to dephospho-CoA, followed by pyrophosphatase action to release 4’-phosphotantetheine and 5’AMP. Red blood cells contain pantothenic acid, pantetheine 4’-phosophate and pantetheine.