37. NUCLEIC ACID AND PROTEIN SYNTHESIS 365 



and by Winnick et al., 7i Melchior and Tarver, 75 and Melchior et a/. 76 The 

 key observations among these studies were that the in vivo process of pro- 

 tein synthesis was endergonic: that a coupled energy yielding reaction was 

 required to make the synthesis proceed. Such a conclusion had been antic- 

 ipated by the studies of Borsook and Dubnoff, 77 showing that reversal of 

 proteolysis could hardly account for protein synthesis, and the prediction 

 of Lipmann. 78 Thus, deprivation of oxygen, 69 presence of respiratory in- 

 hibitors, 74, 79 or uncoupling agents 71 prevented protein synthesis. The rates 

 of incorporation of C 14 -amino acids were shown to be commensurate with 

 the rate of total protein synthesis of various tissues, 35 ' 80 and pure labeled 

 proteins were isolated as products of the incorporation reaction 81 ■ 82 (cf . 

 Dintzis et aZ. 16i ). 



Extension of these in vivo studies revealed that the protein portion of the 

 microsome fraction was the earliest cellular protein fraction to become 

 labeled in a variety of tissues. 83 " 88 The actual site of protein labeling within 

 the microsome fraction was shown by Littlefield et al. 30 ' 35 and Simkin and 

 Work 48 to be the ribosome fraction itself: 



"When whole tumor cells are incubated in ascitic fluid with a C 14 -amino 

 acid, the initial incorporation into whole cell protein is at a rate, e.g., 33 

 /xmoles of leucine per gm. of protein per hour, which is more than adequate 

 to account for the known rate of division of such cells in vivo. The ribonu- 

 cleoprotein particles, which are estimated to contain 8 to 9 per cent of the 

 whole cell proteins, are labeled up to 9 times more rapidly than whole cell 

 proteins. This is consistent with the concept that most of the amino acids 

 incorporated into whole cell proteins pass through the ribonucleoprotein 

 particles." 30 



74 T. Winnick, F. Friedberg, and D. M. Greenberg, Arch. Biochem. 15, 160 (1947). 

 76 J. B. Melchior and H. Tarver, Arch. Biochem. 12, 309 (1947). 



76 J. B. Melchior, M. Mellody, and I. M. Klotz, J. Biol. Chem. 174, 81 (1948). 



77 H. Borsook and J. W. Dubnoff, J. Biol. Chem. 132, 307 (1940). 



78 F. Lipmann, Advances in Enzymol. 1, 99 (1941). 



79 E. Farber, S. Kit, and D. M. Greenberg, Cancer Research 11, 490 (1951). 



80 E. B. Keller, P. C. Zamecnik, and R. B. Loftfield, J. Histochem. and Cytochem. 2, 

 378 (1954). 



81 T. Peters, Jr., J. Biol. Chem. 200, 461 (1953). 



82 R. B. Loftfield and E. A. Eigner, J. Biol. Chem. 231, 925 (1958). 



83 H. Borsook, C. L. Deasy, A. J. Haagen-Smit, G. Keighley, and P. H. Lowy, J. 

 Biol. Chem. 187, 839 (1950). 



84 T. Hultin, Exptl. Cell Research 1, 376 (1950). 

 86 E. B. Keller, Federation Proc. 10, 206 (1951). 



86 V. G. Allfrey, M. M. Daly, and A. E. Mirsky, J. Gen. Physiol. 37, 157, 1953. 



87 V. G. Allfrey, M. M. Daly, and A. E. Mirsky, J. Gen. Physiol. 38, 415, 1955. 



88 M. Rabinowitz and M. E. Olson, Exptl. Cell Research 10, 747 (1956). 



