Inhibition by Puromycin of Amino Acid Incorporation into Protein.

15 Roberts, R. B., P. H. Abelson, D. B. Cowie, E. T. Bolton, and R. J. Britten, Carnegie Institution of Washington Publication 607, Washington, D. C. (1955). 16 The rather low values for threonine and lysine obtained with both labeled aspartic acids in Lemna probably are significant and may indicate a "channeling" of aspartic acid, i.e., a preferential utilization of aspartic acid for incorporation into protein rather than for conversion to threonine or lysine. It will be noted, though, that the labeling of the lysine and the threonine are approximately equal, and that with acetate-2-C'4, all three protein amino acids exhibit nearly the same specific activity. 17 Probable mechanisms underlying the various labeling patterns observed will be discussed elsewhere. 18 Steward, F. C., and J. K. Pollard, Ann. Rev. Plant Physiol., 8, 65 (1957); Virtanen, A. I., Festschrift Arthur Stoll (Basel: Sandoz, 1957) p. 565; Fowden, L., Symp. Soc. Exptl. Biol., 13, 283 (1959); Davies, D. D., J. Hanford, and A. P. Wilkinson, ibid., p. 353; Miettinen, J. K., ibid., p. 210. 19 Bilinski, E., and W. B. McConnell, Can. J. Biochem. Physiol., 35, 357 and 365 (1957). 20 Naylor, A. W., R. Rabson, and N. E. Tolbert, Physiologia plantarum, 11, 537 (1958). 21 Absence of such a steady-state condition may also account for the finding of P. Linko (Acta chem. scand., 12, 101 (1958)) that aspartic acid was the only labeled amino acid in the protein of excised leaves of Convallaria, following their exposure to C14-aspartic acid. 22 Fowden, L., and M. Bryant, Biochem. J., 71, 210 (1959).