water-soluble vitamin essential in animal metabolism. Pantothenic acid, a growth-promoting substance for yeast and certain bacteria, appears to be synthesized by bacteria in the intestines of the higher animals. It was first isolated from liver cells in 1938 and was first synthesized in 1940. It has the following chemical structure:

The vitamin is widespread in nature—especially in yeasts, liver, kidney, eggs, whole grains, and legumes—though it does not exist in its free form in animal tissue. The nature of the bound form was clarified through the discovery and synthesis (1947–50) of the compound pantetheine, which contains pantothenic acid combined with the compound thioethanolamine. Pantetheine is part of two larger compounds (coenzyme A and acyl-carrier protein) that promote a large number of metabolic reactions essential for the growth and well-being of animals. In the absence of pantothenic acid, experimental animals fail to grow, develop skin lesions, and frequently show a graying of the hair. A dietary deficiency severe enough to lead to clear-cut disease has not been described in humans; however, when a person is severely malnourished, deficiency of the vitamin appears to contribute to the observed weakness and mental depression.