Pantothenic Acid

Pantothenic acid was named by Roger Williams who recognized its ubiquitous (greek, pantothene, from all quarters) occurrence in tissues of all organisms and all food sources. There are two twists to the story of its discovery. First is that the coenzyme form, CoA, was discovered long before the vitamin and, second that investigations of the substructure of CoA led to an understanding of how the coenzyme was synthesized. CoA was known to be a dialyzable cofactor essential for the acetylation of sulfonila-mide and choline. Indeed, the 'A' designation in CoA recognized the importance of the acetylation reactions. The first clue to the vitamin's structure came when digests of CoA with intestinal phospha-tase and liver extracts were found to contain ¡-alanine and pantothenic acid as hydrolysis products. Treating CoA with a specific 3' nucleotidase inactivated the coenzyme and a specific pyrophosphatase cleaved the coenzyme to a panthothene-containing product that could be restored to CoA by adenyla-tion with ATP. These studies showed that pantothe-nic acid was an essential component of CoA and had been locked into the structure of a rather complex coenzyme (Figure 6).

Reactivity As a major component of CoA and its derivatives, pantothenic acid is involved in acetyla-tion reactions, which include the synthesis of aceto-acetyl-CoA, a precursor of cholesterol, and the biosynthesis of citrate from acetate. CoA can engage in acyl thiotransfer reactions such as accepting the acetyl groups from lipoic acid and forming acetyl-CoA as well as fatty acyl CoAs. Pantothene is also found as a prosthetic group (4'-pantothene) attached to a serine residue of acyl carrier protein (ACP), which plays a prominent role in the biosynthesis of fatty acids.

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