Effect of methionine on the metabolic fate of liver folates in vitamin B12-deficient rats

Abstract

1. Hepatocytes isolated from vitamin B12-deficient and vitamin B12-supplemented rats were maintained in primary culture and were used to study the effect of methionine on the metabolism of [3H]folic acid and [5-14C]methyltetrahydrofolic acid.2. Vitamin B12levels were reduced by approximately 75% in the hepatocytes from the deficient animals. Total folate and methyltetrahydrofolic acid concentrations were also significantly reduced.3. There was no significanct difference in the uptake and retention of added [3H[folic acid and [5-14C]-methyltetrahydrofolic acid between the hepatocytes of the two groups. The incorporation of14C into phospholipids was reduced by approximately 60% in the vitamin B12-deficient hepatocytes (P< 0.001).4. The addition of methionine to the culture medium doubled the uptake and retention of3H in both groups, but it did not change the amount of water-soluble14C Compounds. In the vitamin B12-deficient hepatocytes mainly methylated folate increased, whereas non-methylated folate increased in the hepatocytes of the control animals. A tenfold increase of14C incorporated into phospholipids was found in both groups after methionine was added.5. Demethylation of methyltetrahydrofolic acid, the intracellular retention of folate and the utilization of liberated methyl groups, for example in the methylation of phospholipids, were highest in the presence of both methionine and vitamin B12suggesting an intimate co-ordination between these two substances in the regulation of folate metabolism.