On the Significance of Measurements of Amino Acid Incorporation into the Proteins of Cell-free Preparations.

pea seedlings incorporate a variety of C14-amino acids into their protein. The incorporation is promoted by adenosine triphosphate, by a mixture of amino acids, by magnesium and potassium ions (5), and by the nucleosides derived from ribonucleic acid (6). Amino acid incorporation is inhibited by adenosine diphosphate, by amino acid analogues, by rubidium ions, by certain purine analogues, and by treatment of the cell-free extract with ribonuclease (4, 5, 6). The properties of the incorporation system, therefore, resemble in many respects the properties of similar cell-free systems prepared from mammals (2, 3, 7) and bacteria (1). Recently, however, the author has received several inquiries as to whether amino acid incorporation in such cell-free systems might be due to the presence of bacteria in the preparations. Although prelimi-