抄録
NTS cell-line is a pure colonal clone separated from mass culture cells of newborn rat cerebellum which were maintaining in continuous cultivation since 57 months. This cell-line was cultured in such a way that this appeared to be dependent upon vitamin B_<12>. Methionine was replaced by homocysteine in the medium and the cells survived and proliferated only when vitamin B_<12> was added. The terminal reaction in methionine biosynthesis involves the transfer of a methyl from methyltetrahydrofolate to homocysteine. The cells were harvested at the indicated time intervals and assayed for this methyltransferase activity as described in Weissbach's method. The levels of 5-methyltetrahydrofolate-homocysteine methyltransferase activity were elevated in maximum level in 24 hours incubation. Elevated enzyme levels were also observed in cells cultured in the medium containing methionine. These levels were not related with the addition of homocysteine. This only occured when vitamin B_<12>, especially methyl-B_<12> was also included in the medium. The activities of this methyl-transferase wer enot elevated on cell-free system with vitamin B_<12>, and inhibited on NTS-cells in the medium containing puromycin with vitamin B_<12>. It is assumed from above results that the 5-methyltetrahydrofolate-homocysteine methyltransferase in NTS cells might be induced directly by the vitamin B_<12>.
