The inhibition of accumulation of [1-14C]glycine and its incorporation into protein of Ehrlich ascites-carcinoma cells by DL-methionine.

1. By incubation of Ehrlich ascites-carcinoma cells in vitro with [1-(14)C]glycine the relation between the uptake of glycine and its incorporation into protein was examined. 2. With dl-methionine as a competitive inhibitor, there was not only a decrease in uptake of this amino acid, but also inhibition of its incorporation into protein. 3. It is only in its initial stage that the increase in incorporation is accompanied by increase in intracellular concentration of free glycine. Further increase in the amino acid pool has no effect on protein synthesis. 4. Even with a high cell concentration of glycine, methionine produces a decrease both in the uptake and its incorporation. This suggests that the inhibition of incorporation of glycine by methionine is due, not only to decrease in its intracellular concentration, but also to changes in other processes responsible for protein synthesis.