The effect of methionine on the metabolism of serine and glycine in vitamin B-12-deficient rats.

The effect of methionine supplementation on glycine and serine metabolism was studied in vitamin B-12-deficient rats which received only 0.2% methionine in the diet. In the perfused liver, incorporation of the C-2 of glycine to the C-3 of serine was increased by addition of methionine to the perfusate. The oxidation of [1-14C]glycine to 14CO2 was however depressed. Unlike methionine, glycine did not have any significant effect on the liver folate coenzyme distribution. Oxidation of [3-14C]serine to 14CO2 both in vivo and in perfused liver was increased by methionine. A major portion of the C-3 radioactivity however was recovered in glucose. Data presented indicate that the rate of oxidation of [2-14C]histidine to 14CO2 is a more sensitive indicator of folate deficiency than the rate of oxidation of [3-14C]serine to 14CO2 although both are presumably tetrahydrofolate dependent.