[Folic acid metabolism in rapidly growing tissues: synthesis of pteroylpolyglutamates]

Pteroylpolyglutamates are regarded as the functional coenzyme form of folate: hence their synthesis may represent important regulatory step in the folate-dependent processes. To verify this hypothesis the pteroylpolyglutamate content was studied in rapidly growing tissues, which require a large availability of folate coenzymes, essential as carbon atom donors in the synthesis of purine and pyrimidine nucleotides and in the metabolism of some aminoacids. In the developing chick embryo, the higher polyglutamates are the only folate forms present and their content increases progressively during the development of the embryo. In rat liver regenerating after partial hepatectomy the higher polyglutamate forms decrease below the normal values from 12 to 72 h after the operation; the normal values are restored after 180 h. The initial drop is not related to a lower synthesis, but to a greater utilization of these coenzymes during the early periods of regeneration, when biosynthetic processes are markedly increased. In fact the content of polyglutamates in regenerating liver can be maintained at normal levels by increasing the availability of precursors via folic acid administration to hepatectomized rats.