Radiophosphorus and Nucleic Acids 



181 



proportion of organic phosphate, which is responsible at 

 least in part for the fact that the amount of reactive pentose 

 in the ribonucleotide fraction is invariably less than is 

 expected on the basis of the phosphorus content. 



Table VI 



Concentrations and Activities of Phosphorus Fractions Separated 



by lonophoresis from the ribonucleotide fraction in a schmidt- 



Thannhauser Separation of Rat Liver Tissue 



10 /iC. ^^P per 100 g. body weight were injected two hours before kilhng. 



Smellie has also applied the ionophoresis procedure for 

 ribonucleotide separation to tissue fractions from the livers 

 of rats which had received radiophosphate by injection two 

 hours previously, in order to determine the individual specific 

 activities of the four nucleotides derived from RNA. The 

 results of such an experiment are shown in Table VI, from 

 which it will be seen that in the ribonucleotide fraction ob- 

 tained from the Schmidt-Thannhauser separation of rat liver, 

 the uridylic acid has a higher activity than the purine nucleo- 

 tides, and all nucleotides have a lower activity than the 

 inorganic phosphate from "phosphoprotein" and the organic 

 phosphate which accompanies it. 



Since ribonucleic acid occurs in several different cellular 

 components it is obviously desirable to compare the activities 

 of the RNA phosphorus of different origins. This has been 

 done by W. M. Mclndoe and R. M. S. Smellie using rat liver 

 tissue for the isolation of nuclei by the citric acid method of 

 Mirsky and Pollister (1946) and for the isolation of cytoplas- 

 mic particles from a homogenate in saline by the method of 



