Folacin is the generic descriptor not only for the original vitamin, folic acid, but also for related compounds that qualitatively show folic acid activity.
Sulfonamides are analogs of the folic acid biosynthetic intermediate PABA and are widely used as antibacterial agents. By competing with PABA, sulfonamides prevent folic acid synthesis so that microorganisms cannot multiply, with the result that an important source of folic acid to the animal is reduced or eliminated.
Folic acid is widely distributed in nature, almost exclusively as THF acid derivatives. Only limited amounts of free folic acid occur in natural products, and most feed sources contain predominantly polyglutamyl folic acid. Soybeans, other beans, nuts, some animal products and citrus fruits are good sources. Cereal grains, milk and eggs are generally poor sources of the vitamin. Folic acid is abundant in green leafy materials and organ meats.
