THE USE OF RADIOPHOSPHORUS IN THE 

 STUDY OF THE NUCLEIC ACIDS* 



J. N. DAVIDSON 



This paper is an account of recent work carried out by a 

 group of biochemists in Glasgow using ^^P for nucleic acid 

 work. 



When radioactive phosphorus is used as a tracer in experi- 

 ments on the nucleic acids and nucleoproteins, it is possible 

 when dealing with moderately large amounts of tissue to 

 isolate the nucleic acids in a purified state before determining 

 specific activities; but when only minute amounts of tissue 

 are available attempts have been made to determine specific 

 activities on tissue fractions rather than on isolated sub- 

 stances. Thus when a sample of liver tissue, from which acid 

 soluble phosphorus and lipid phosphorus have been extracted, 

 is incubated in alkali in accordance with the usual Schmidt- 

 Thannhauser (1945) procedure, it has been assumed by some 

 authors that the precipitate obtained on acidifying the 

 alkaline digest will give the activity of the deoxyribonucleic 

 acid (DNA), while the supernatant fluid containing the nucleo- 

 tides derived from ribonucleic acid (RNA) will give the 

 activity of the RNA. That this is by no means the case is 

 shown from Tables I and II. 



In the first place the acid supernatant fluid in the Schmidt- 

 Thannhauser separation contains, in addition to ribonucleo- 

 tides, a minute amount of inorganic phosphate usually 

 supposed to be derived from "phosphoprotein." This "phos- 

 phoprotein phosphorus" has a much higher activity than has 

 the ribonucleotide phosphorus (Davidson et al., 1949) but its 

 presence is frequently disregarded. Moreover, comparisons 



♦This work was supported by grants from the Medical Research Council 

 and the British Empire Cancer Campaign, to whom grateful thanks are due. 



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