PEPTIDES AND PROTEINS I09 



proteins provided the appropriate nucleic acid framework is 

 made available. 



By using materials enriched with radio-active phosphorus 

 (P^2), several workers have measured the turnover rate of 

 nucleic acid phosphate groups and the effect thereon of 

 variations in the rate of protein synthesis. All the results 

 reported so far are based on isotopic analyses of impure 

 preparations of nucleic acid and must therefore be treated 

 with caution since Davidson and his colleagues have shown 

 that unequivocal results are obtained only if these substances 

 are rigorously freed from contaminating materials before de- 

 termining their P^^ content [7]. Spiegelman and Kamen [39] 

 have found that the fermentation of glucose by washed sus- 

 pensions of yeast previously grown in the presence of in- 

 organic phosphate enriched with P^^ did not cause any 

 decrease in the concentration of P^^ in the nucleic acid 

 fraction of the cells. However, if NHt was added to the 

 system, protein synthesis and budding occurred and the P^^ 

 content of the nucleic acids decreased. A similar decrease 

 took place during the adaptive formation of maltase. The 

 proposal was therefore advanced that the energy in the phos- 

 phate bonds of the nucleic acid could be utilized in transfer 

 reactions for the synthesis of peptide bonds. 



From this brief survey it will be apparent that whilst there 

 is some experimental evidence that nucleic acids mediate 

 protein synthesis, our present conceptions of the cellular 

 organization controlling and bringing about such syntheses 

 are purely speculative (see [51] for a critical analysis of pos- 

 sible mechanisms for the synthesis of proteins). 



REFERENCES 



1. Agren, G. (1948), Acta chem. Scand., 2, 611 



2. Bovarnick, M. R, (1942),^. biol. Chem., 145, 415 



3. Caldwell, P. C. and Hinshelwood, C. (1950), J. chem. Soc, 



3156 



4. Callow, A. B. and Robinson, M. E. (1925), Btochem. y., 19, 19 



5. Chattaway, F. W., Dolby, D. E., Hall, D. A. and Happold, 



F. C. (1949), Biochem. J., 45, 592 



6. Conn, E. E. and Vennesland, B. (195 1), Nature^ 167, 976 



