Functions of Folacin
The major role of the enzymatically active forms of folacin is in the transfer of 1-carbon unit to various compoumds in the syn thesis of the purines and pyrimidines of DNA and RNA, and in amino acid interconversions.
Some of the folacin-requiring reactions use THFA, which serves as an acceptor of a 1-carbon unit from the substrate (as in the conversion of serine to glycine). The resulting THF A derivatives then serve as donors of 1-carbon units in other reactions, such as the synthesis of the nucleotide thymidylate (No,lO-methylene THF A), which is part of the DNA structure. Similarly, No,lO-methenyl THFA and N10-formyl THFA contribute a carbon to the ring structure of purine bases.
The amino acid, histidine, requires THFA for its complete utilization. When it is not available, the intermediary product, formiminoglutamic acid (FIGLU), is excreted in the urine. FIGLU excretion levels can then be used to determine folacin nutritional status. However, increased excretion of FIGLU is only an indirect, nonspecific indication of a possible folacin deficiency. Because the major function of folacin is in DNA and RNA synthesis and indirectly affects protein synthesis, the manifestations offolacin deficiency are most pronounced in rapidly grmving tissues or in tissues ,vith rapid cell turnover. Folacin deficiency in humans results in megaloblastic anemia, glossitis, and gastrointestinal disturbances. Because of the interdependence of vitamins BB ascorbic acid, and folacin, the anemia found in these deficiency diseases may be similar and may respond to treatment with one or several of these nutrients. It should be pointed out, however, that even though the anemia in pernicious anemia may be relieved by folic acid, only vitamin BIz cures the neurologic symptoms.
