Tetrahydrofolate-dependent Enzyme Activities of the Rat Liver in Riboflavin Deficiency

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Abstract
Urinary excretion of formiminoglutamic acid (FIGLU) following an oral, intraperitoneal, intramuscular, or intravenous load with L-histidine-monohydrochloride was markedly reduced in rats when fed on a riboflavin deficient diet for 11-30days. The assay of tetrahydrofolate-dependent enzyme activity of the liver revealed that there were a marked decrease in the activity of N5,10 methylenetetrahy-drofolate reductase and a considerable decrease in that of N5 methyltetra-hydrofolate transf erase of the liver from the ribof lavin deficient rats. Results of bioassay using Lactobacillus casei, Streptococcusfaecalis and Pediococcus cerevisiae of f olate compounds of the liver revealed a tendency toward relative increase in folate derivatives other than N5 methyltetrahydrofolate in the liver of riboflavin deficient rats. From these results it was assumed that a decreased activity in both the N5,10 methylenetetrahydrofolate reductase and N5 methyltetrahydro-folate transf erase was induced by ribof lavin deficiency, and then that the decrease in the activity of the both enzymes caused an accumulation of tetrahydrofolate compounds other than N5 methyltetrahydrofolate, thus affording a relatively large amount of free tetrahydrofolate available for the formiminotransferase reaction, with a consequence of rapid conversion of FIGLU into glutamic acid. Free methionine levels of the liver was not found to be increased but slightly decreased in riboflavin deficient rats as compared with those of control rats.