METABOLISM OF THE NUCLEIC ACIDS 399 



such a technique,-'"^'* but the danger of contamination of such fractions 

 with highly active non-nucleic acid phosphorus has been stressed by Bar- 

 num et al.,^^ Friedkin and Lehninger/^ Jeener,"'^^ and by Jeener and 

 Szafarz,^^ who like Davidson et a/.^-'*" have shown that there is no justifi- 

 cation for the assumption that the specific activities of the nucleic acid 

 fractions obtained by the Schmidt-Thannhauser technique is a measure 

 of the specific activities of the nucleic acids. In the ribonucleotide fraction, 

 this discrepancy is due to the presence of non-nucleotide phosphorus of very 

 much higher activity than the nucleotide phosphorus itself.^'' Jeener and 

 Szafarz^^ and Szafarz and Paternotte''^ have used paper chromatography 

 of the ribonucleotide fraction in an attempt to rid it of contaminating 

 non-nucleotide phosphorus, but the most satisfactory technique seems to 

 be that of Davidson and Smellie,^* who have subjected the ribonucleotide 

 fraction to ionophoresis, thus separating its constituent nucleotides and at 

 least six other phosphorus-containing compounds, one of which is inorganic 

 phosphate. 



b. The Relative Incorporations of Isotopic Phosphorus into the PNA and 

 DNA of Different Tissues 



Generally speaking, the uptake of P^^ by the PNA of resting tissues is 

 considerably greater than the corresponding value for DNA. This dif- 

 ference is illustrated in Table V of Chapter 25, where the ratio of P^- in 

 PNA to that in DNA is less than unity only in tissues such as regenerating 

 or fetal liver where the metabolic activity of the DNA is greatly increased. 

 This table shows that the observed ratios vary considerably from tissue to 

 tissue and also with the different times after administration of the isotope, 

 indicating that the relationship between the PNA and DNA metabolic 

 activities is not constant from tissue to tissue or even mthin the same 



" R. M. Campbell and H. W. Kosterlitz, /. Endocrinol. 6, 171 (1949). 



30 B. E. Holmes, Brit. J. Radiol. 22, 487 (1949). 



'^ B. E. Holmes, Abstr. 1st Intern. Biochem., Cambridge, Engl. p. 263 (1949). 



32 W. Hull and P. L. Kirk, J. Gen Physiol. 33, 325 (1950). 



33 W. Hull and P. L. Kirk, /. Gen. Physiol. 33, 335 (1950). 

 3^ W. Hull and P. L. Kirk, J. Gen. Physiol. 33, 343 (1950). 



3^ C. P. Barnum, C. W. Nash, E. Jennings, O. Nygaard, and H. Vermund, Arch. 



Biochem. 25, 37Q (1950). 

 3« M. Friedkin and A. L. Lehninger, J. Biol. Chem. 177, 775 (1949). 

 3' R. Jeener, Nature 163, 837 (1949). 



38 R. Jeener, Bull soc. chim. biol. 31, 731 (1949). 



39 R. Jeener and D. Szafarz, Experientia 6, 59 (1950). 



*" J. N. Davidson, Ciba Conf. on Isotopes in Biochem., London p. 175 (1951). 



*^ R. Jeener and D. Szafarz, Arch. Biochem. 26, 54 (1950). 



^2 D. Szafarz and C. Paternotte, Bull. soc. chim. biol. 33, 1518 (1951). 



