METABOLISM OF THE NUCLEIC ACIDS 403 



substances giving rise to one-carbon compounds, carbon 4 is derived from 

 the carboxyl group of glycine, carbon 5 from the methylene group of 

 glycine, and carbon 6 from carbon dioxide. It has also been shown that 

 nitrogen atoms 1, 3, and 9 are derived from the amino-nitrogen pool and 

 nitrogen 7 from glycine. 



A suitable choice of labeled precursor thus enables the metabolism of the 

 individual purine bases to be studied from several different aspects. 



b. Studies with Formate-C^^ 



Several authors have used formate-C" in studies of nucleic acid metabo- 

 lism. Drochmans et al.^^ have shown that, after administration of labeled 

 formate to rats, the activity of the PNA purines from different tissues 

 decreased in the order intestine, kidney, spleen, liver, pancreas, and testis. 

 No differentiation was found between the isomeric forms of adenylic and 

 guanylic acids in anv of these tissues, and in all tissues except spleen the 

 activity of the adenylic acid was appreciably greater than that of the 

 guanylic acid. Totter et al}"^ have studied the utilization of formate-C" 

 by the mononucleotides of visceral PNA and DNA in rats and chickens. 

 They found that there was appreciable uptake of isotope by the purine 

 nucleotides of both nucleic acids while, as expected, the pyrimidine nucleo- 

 tides showed little activity. In the rat viscera, the adenylic acids of both 

 PNA and DNA exhibited a considerably higher uptake of isotope than did 

 the corresponding guanylic acids. Similar observations on the higher 

 incorporation of C^^ from formate into the adenine than into the guanine of 

 liver nucleic acids have been recorded by Goldthwait,^^ Smellie et al.,^^ 

 and by Drysdale et al.^" 



The uptake of formate-C'^ by the purines of DNA from different tissues 

 in normal mice and in mice with mammary carcinomata has been the 

 subject of research by Payne et a^,^"'^^ who have observed that the DNA of 

 spleen and intestine is much more active than that of liver, the relative 

 values being: spleen 10, intestine 9.6 to 9.9, and liver 0.3 to 0.4. These 

 values are similar to those found for the same tissues with P^- (Table I). 



The relative rates of renewal of the purines of PNA and DNA in different 

 tissues are sunmaarized in Table V of Chapter 25. The activity of PNA in 

 general exceeds that of DNA, and the ratios are similar to, although slightly 

 lower than, those obtained with P^-. 



^* P. Drochmans, D. H. Marrian, and G. B. Brown, Arch. Biochem. and Biophys. 39, 



310 (1952). 

 " J. R. Totter, E. Volkin, and C. E. Carter, J. Am. Chem. Soc. 73, 1521 (1951). 

 68 D. A. Goldthwait, Proc. Soc. Exptl. Biol. Med. 80, 503 (1952). 

 " R. M. S. Smellie, W. M. Mclndoe, and J. N. Davidson, Biochem. et Biophys. Acta 



11, 559 (1953). 

 6" G. R. Drysdale, G. W. E. Plaut, and H. A. Lardy, /. Biol. Chem. 193, 533 (1951). 



