Effects of Dietary Methionine and Vitamin B12 Deficiency on Folate Metabolism

S ummary . Glutamate formimino transferase activity (GFA) and liver folic acid and vitamin B₁₂ levels were decreased in rats fed diets deficient in methionine and vitamin B₁₂. The addition of either methionine or vitamin B₁₂ resulted in a rise in GFA and in liver folate levels. However, L. casei serum folate was not affected by the dietary level of vitamin B₁₂ or methionine, but the S. faecalis serum folate decreased as the level of dietary methionine and vitamin B₁₂ was increased. The results of these studies do not appear to support the concept that vitamin B₁₂ deficiency results in a 'pile-up' of N⁵-methyl folate but suggests that it induces folate deficiency. Also the results suggest that the effect of vitamin B₁₂ on folate metabolism may be mediated via methionine metabolism.