Incorporation of Labeled Amino Acids into Serum and Tissue Proteins from Normal and X-Irradiated Mice

Incorporation of ${\rm H}^{3}\text{-}{\rm L}\text{-phenylalanine}$ and ${\rm H}^{3}\text{-}{\rm L}\text{-tryptophan}$ into serum and tissue proteins has been studied in normal and X-irradiated mice. After doses of 700 R and 1000 R, incorporation was increased rather than decreased. A higher specific activity was found in the fractions that decrease in concentration after irradiation. A decrease in the pool size and specific activity of free amino acids in the liver or spleen cannot be responsible for this effect. Thus, the high specific activity of fractions such as γ-globulins, which are decreased in concentration after irradiation, would indicate an increased synthesis.