Vitamin B12 Deficiency in the Rat: Effect on Serum Folate and Liver Formiminotransferase Activity

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Abstract
Serum folate and vitamin B12 levels and the activity of the enzyme, glutamate formiminotransferase, were determined in young male rats fed diets with and without added vitamin B12. All diets were low in choline and methionine. Vitamin B12 deficiency resulted in higher total serum folate levels. From the differential microbiological assays performed for serum folate activity (S. faecalis and L. casei assays), the results of this study support the view that in vitamin B12 deficiency there is a greater proportion of the total serum folate circulating as the N5-methyl-tetrahydrofolic acid form. The increased urinary excretion of formiminoglutamic acid (FIGLU) observed previously in vitamin B12 deficiency was also noted in the present study. However, it was demonstrated for the first time that the activity of the enzyme, glutamate formiminotransferase, was markedly decreased in vitamin B12 deficiency. A decrease in the activity of this enzyme would be expected to result in increased urinary FIGLU excretion. The possible biochemical defects resulting in lowered activity of formiminotransferase and increased excretion of urinary FIGLU in vitamin B12 deficiency are discussed.