Purine incorporation into pentose nucleotides of the rat.

Earlier communications from this laboratory (l-3) have reported several studies of purine metabolism in which the individual purines were isolated by chemical procedures from nucleic acid preparations obtained either by salt extraction of desiccated tissues or by the Schmidt and Thannhauser (4) procedure for separation of the pentose (PNA) and desoxypentose nucleic acids (DNA) (5). With the recognition by Carter and Cohn (6-9) that two adenylic acids (a and b) and two guanylic acids (a and b) are obtainable from pentose nucleic acids it became desirable to investigate the possibility of metabolic differences between the isomeric purine nucleotides. The ion exohange technique of Cohn (7, 9) for the separation of the nucleotides is applicable on a very small scale and its adoption would also permit metabolic studies in single animals and on individual tissues. The scale chosen will permit the isolation of quantities of each nucleotide which represent at least 0.5 to 1.0 mg. of nitrogen. This permits the study of precursors labeled with heavy nitrogen (N16) as well as with radioactive carbon (CY4). Since the beginning of this study the isolation of isomers of the pyrimidine nucleotides has been achieved (10, ll), but the facility with which they are interconverted (11) lessens the importance of their separation in metabolic studies. In the majority of our previous studies with N15-labeled adenine and other purines, the purine has been administered at a level of at least 0.2 mM per kilo of body weight per day, an amount corresponding to somewhat less than one-half of the lowest value given for the excretion of allantoin by the rat (12). However, very little uncombined adenine is to be found in normal diets, and work with intact nucleic acids (13), and subsequently with the constituent purine nucleotides,l has shown that