American Journal of Clinical Nutrition, Vol 20, 311-316, Copyright © 1967 by The American Society for Clinical Nutrition, Inc.

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

¹ From the Department of Foods and Nutrition and the Department of Medicine, University of Wisconsin, Madison, and the Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts

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.