Purine Metabolism in Mouse Ascites Tumor Cells: III. In Vivo Incorporation of Preformed Purines into Nucleotides and Polynucleotides^*

The in vivo incorporation of C¹⁴-labeled adenine and guanine compounds into nucleic acids and acid-soluble nucleotides was studied in Ehrlich ascites cells for incubation periods of 10–60 minutes. Corresponding to results in vitro, nucleoside was incorporated more rapidly than nucleotide, and nucleoside diluted the incorporation of nucleotide into nucleic acids more than nucleotide diluted that of nucleoside. Adenine was incorporated less rapidly than its nucleoside and nucleotide, but guanine was incorporated as well or better than guanosine and GMP. The labeling of acid-soluble nucleotides from incorporations of adenine and guanine indicated that a part of the free base was converted to mononucleotide without passing through nucleoside.

During a 10-minute period, not more than 20 per cent of totally labeled guanosine-C¹⁴ or GMP-C¹⁴ and not more than 41 per cent of AMP-C¹⁴ was incorporated into the corresponding nucleic acid nucleotide with riboside linkage intact. Some breakage occurred before and/or during incorporation of the injected precursor into acid-soluble compounds. The rate and pattern of labeling differed between base and sugar, nucleotide and nucleoside precursors, and guanine and adenine precursors. Deoxyribotides had a higher proportion of their radioactivity in the sugar moiety than did the corresponding ribotides.