Intracellular amino acids and protein synthesis in Hela cells.

(1) When the intracellular amino acid pool is prelabelled and subsequently chased in non-radioactive medium, the radioactivity of the amino acid pool is not found to have been incorporated into protein. (2) Leucine transport into Hela cells is reduced in the presence of 10 mM valine in the medium. This results in a lower specific radioactivity of leucine in the intracellular amino acid pool. However, neither the overall rate of protein synthesis nor the incorporation of radioactive leucine into protein is affected. From these experiments it is concluded that incoming amino acids entering the intracellular amino acid pool are not used for de novo synthesis of protein.