Vitamin B12and methyl-group synthesis

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Abstract
Methionine stimulated growth of Ochromonas mal-hamensis on simplified media containing either inorganic N or a complete amino acid mixture, both in presence and absence of vitamin B12-The methionine could be replaced by homocystine, homocysteine, gly-cine or serine only when vitamin B12 was present. Transmethylation appears to be ruled out, since no response was obtained with choline. Inhibition of growth of the organism by ethionine was completely reversed by methionine. Both growing cells and cell-free preparations from Ochromonas grown with adequate B12 used Cl4 from the a group of glycine for incorporation into methionine, while cells grown with a limited supply of the vitamin did not have this ability. It appears that vitamin B12 acts specifically in methyl group syntheses.