Amino Acid Incorporation by Intact and Disrupted

Although much has been learned in recent years concerning amino acid incorporation into protein, the mechanism of the process has remained obscure. This is due partly to the complexity of the problem and partly to the lack of experimental systems sufficiently simple and free from extraneous reactions so that mechanism studies can be performed with confidence. The experiments of Littlefield and Keller (a), however, have shown that ribonucleoprotein particles from Ehrlich ascites tumor cells can incorporate amino acids into their protein in the presence of ATP,’ Mg++, guanosine phosphates, and the “pH 5 proteins” (3) of liver or of ascites cells. This finding, together with the apparent simplicity of ribonucleoprotein particles from various sources (2, 4, 5), suggests that such isolated particles may be part,icularly suitable for studies on the mechanism of amino acid incorporation into protein. In view of the limited availability, in quantity, of ascites tumor particles, experiments were initiated to determine whether ribonucleoproiein particles from other sources are likewise capable of incorporating amino acids into protein. It was also of interest to know whether such incorporation is similar to that of ascites particles and whether the ribonucleoprotein particles can incorporat,e nucleotides into their ribonucleic acid. As is reported in this paper, it has been found that isolated ribonucleoprotein particles from yeast (4) and from pea seedlings (5) are indeed able to incorporate amino acids into their protein and nucleotides into their ribonucleic acid. However, the properties of the incorporation process in pea seedling ribonucleoprotein particles differ somewhat from those of ascites particles, and the pea seedling particles have the surprising ability to catalyze an amino acid-promoted exchange of both pyrophosphate and AMP with ATP. In addition, preliminary studies have been made on