Originally published in Acta Physiol. Scand. 5, 237 (1943). 



67. R4TE OF FORMATION OF NUCLEIC ACID 

 IN THE ORGANS OF THE RAT 



G. Hevesy and J. Ottesen 

 From the Institute of theoretical Physics, University of Copenliagen 



The rate of formation of nucleic acid of the thymus nucleic acid type 

 was investigated in the organs of the rat by administering labelled 

 phosphate to rats and by determining the labelled P content of the 

 desoxyribose nucleic acid extracted from the organs after the lapse of 

 some days. The percentage of labelled nucleic acid present indicates 

 the percentage of the total nucleic acid of the organs which is built 

 up in the course of the experiment, as described in this note. 



Preliminary figures on the rate of formation of nucleic acid in some 

 of the organs of the rabbit were communicated at an earlier date (Hahn 

 and Hevesy, 1940). Data are furthermore available on the rate of for- 

 mation of labelled "nucleoprotein" in some organs of the mouse (Tuttle, 

 Erf and Lawrence, 1941). In our previous work, we extracted the 

 nucleic acid with sodium chloride solution. Tuttle and his colleagues 

 removed the acid soluble and the phosphatide P fractions from the 

 organs investigated and considered the residual P to be phosphorus of 

 the "nucleoprotein" fraction. Extended studies carried out in this 

 laboratory lead to the result that it is hardly possible to obtain nucleo- 

 protein sufficiently purified from non-nucleoprotein phosphorus by the 

 last mentioned procedure. Muscles and other organs of the frog con- 

 taining labelled P were treated for weeks daily alternately with tri- 

 chloroacetic acid solution and with ether alcohol mixtures. The specific 

 activity of the remaining "nucleoprotein" P was determined subse- 

 quently. It was found much higher than the specific activity (activity 

 per mgm P) of phosphorus obtained from properly purified nucleic acid. 

 As shown in this note, the rate of formation of nucleic acid in most organs 

 is very slow and, correspondingly, the specific activity of the nucleic 

 acid P few hours and even some days after the administration of labelled 

 P is low also. 



After the lapse of 2 hours, 1 mgm nucleic acid Pof the liver of the rat, 

 for example, contains but 2 • 10^^ per cent of the labelled phosphorus 

 administered, while the corresponding figure for 1 mgm acid solul)le P of the 

 liver is about 1 per cent. If only 10"^ part of the isolated nucleic acid P 



