INCORPORATION OF THE 2-RING CARBON OF HISTIDINE INTO FOLYLPOLYGLUTAMATE COENZYMES

The purpose of these experiments was to study the distribution of the single carbon atoms in folate coenzymes that had been derived from [2-ring-C-14] histidine. A rat that had been fed a low methionine diet for five weeks was injected intravenously with 100-mu-Ci of [2-ring-C-14] histidine. After 2.5 minutes, the liver was removed, extracted, and the extract analyzed by DEAE column chromatography. Fractions were counted and assayed using Lactobacillus casei and Streptococcus faecalis. Radioactivity from ring carbon histidine was found only in methyl-H4folates and none in formyl-H4folates. This represents the first report showing the direct incorporation of carbons into folate coenzymes in vivo. Approximately 1/250th of the methyl carbon of each 5-methyl-H4PteGlu5 and 6 was radioactive. The identification of C-14 labeled methyl group was established by conversion of the methyl group to labeled formaldehyde by methylene-H4folate reductase. The radioactive labeling of the methyl group in proportion to the microbiological activity was the same for the penta- and hexaglutamates. This shows that these two polyglutamates participated equally in the metabolism of the carbon derived from histidine.