Metabolism of 9-β-D-Arabinofuranosyladenine by Mouse Fibroblasts1

The metabolism of 9-β-D-arabinofuranosyladenine (araA) by exponentially growing mouse fibroblasts in suspension culture has been investigated. After a 4-hr incubation with 0.1 mM [3H]araA, only 0.14% of the total 3H was in the cell fraction, whereas 48% of the araA in the medium had been deaminated to 9-β-D-arabinofuranosylhypoxanthine. Of the cellular 3H, 80% was acid soluble, and of these 75% was associated with adenine nucleotides and 25% was associated with nucleosides. 9-β-D-arabinofuranosylhypoxanthine comprised 80% of the labeled nucleosides, the rest being araA or adenosine. Following dephosphorylation of the acid-soluble fraction, 80% of the 3H was in araA and 9-β-D-arabinofuranosylhypoxanthine, and 18% was in adenosine. Ninety % of the 3H in the adenine-containing triphosphates was shown to be in arabinosyl compounds, and the remainder was in adenosine and deoxyadenosine. The concentration of cellular 9-β-D-arabinofuranosylade-nine 5'-triphosphate was calculated to be 20 μM. The RNA fraction contained 16% of the total cellular 3H. Over 90% of the 3H was associated with the adenosine 2‘(3’)-phosphate fraction; the remainder was nucleoside, mainly araA. When the adenosine 2‘(3’)-phosphate fraction was dephosphorylated, nearly 70% of the 3H was contained in adenosine, indicating extensive metabolism of araA. The remaining 3H was associated with arabinosyl compounds. The DNA fraction contained 2% of the cellular 3H. After degradation to 5'-monophosphates, the 3H was found mainly in 9-β-D-arabinofuranosyladenine 5'-phosphate; after dephosphorylation 95% of the 3H was in araA. Following degradation to 3'-monophosphates and terminal nucleosides, the majority of the 3H was associated with 9-β-D-arabinofuranosyladenine 3'-phosphate, whereas a minor portion was in the nucleoside. These results suggest that, after incubation with mouse fibroblasts, most of the exogenous araA is deaminated and remains in the medium or is otherwise metabolized. A small amount is phosphorylated to arabinosyl nucleotides that attain inhibitory cellular concentrations, and some 9-β-D-arabinofuranosyladenine 5'-triphosphate is subsequently incorporated in internucleotide linkage into DNA.