Effect of Methionine on Hepatic Folate Metabolism in Rats Fed a Vitamin B12- and Methionine-Deficient Diet 1

Summary

The effect of methionine on the metabolism of hepatic folate in the vitamin B12- and methionine-deficient rat was investigated. The liver uptake of a labeled dose of PteGlu by the deficient rats remained constant at approximately 8% between 2 and 24 hr after the injection. At the early time periods (2 and 4 hr), the major labeled folate derivative was 5-methyl-H₄PteGlu and no appreciable synthesis of labeled pteroylpoly-y-glutamate was detected. An injection of methionine (37 mg) suppressed the level of 5-methyl-H₄PteGlu and increased the synthesis of pteroylpoly-γ-glutamates. Methionine also increased the total net hepatic uptake of the labeled folate dose. The increased net uptake was entirely due to increased synthesis of pteroylpolyglu-tamates. These results are best explained by the methyl trap hypothesis for B12/folate interrelationships.