The most important function of CoA is to act as a carrier mechanism for carboxylic acids (Lehninger, 1982). Such acids, when bound to CoA, have a high potential for transfer to other groups, and such carboxylic acids are normally referred to as "active." The most important of these reactions is the combination of CoA with acetate to form "active acetate" with a high-energy bond that renders acetate capable of further chemical interactions. The combination of CoA with two-carbon fragments from fats, carbohydrates and certain amino acids to form acetyl-CoA is an essential step in their complete metabolism because the coenzyme enables these fragments to enter the TCA cycle. For example, acetyl-CoA is utilized directly by combining with oxaloacetic acid to form citric acid, which enters the tricarboxylic acid (TCA) cycle.
Coenzyme A, along with ACP, functions as a carrier of acyl groups in enzymatic reactions involved in synthesis of fatty acids, cholesterol and other sterols; oxidation of fatty acids, pyruvate and alpha-ketoglutarate; and biological acetylations. In the form of acetyl-CoA, acetic acid can also combine with choline to form acetylcholine, a chemical transmitter at the nerve synapse, and can be used for detoxification of various drugs, such as sulfonamides.
Decarboxylation of alpha-ketoglutaric acid in the TCA cycle yields succinic acid, which is then converted to the "active" form by linkage with CoA. Active succinate and glycine are together involved in the first step of heme biosynthesis. Pantothenic acid also stimulates synthesis of antibodies, which increase resistance of animals to pathogens. It appears that when pantothenic acid is deficient, the incorporation of amino acids into the blood albumin fraction is inhibited, which would explain why there is a reduction in the titer of antibodies (Axelrod, 1971).
