Turriani M, Pesi R, Nardone A, Turchi G, Sgarrella F, Ipata PL, Tozzi MG. Cytosolic 5'-nucleotidase/nucleoside phosphotransferase: a nucleoside analog activating enzyme?
JOURNAL OF BIOCHEMICAL TOXICOLOGY 1994;
9:51-7. [PMID:
8151632 DOI:
10.1002/jbt.2570090108]
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Abstract
Nucleoside phosphotransferase acting on inosine and deoxyinosine has been partially purified from cultured Chinese hamster lung fibroblasts (V79). The activity is associated with a cytosolic 5'-nucleotidase acting on IMP and deoxyIMP. The transfer of the phosphate group from IMP to inosine catalyzed by this enzyme was activated by ATP and 2,3-bisphosphoglycerate. Inosine, deoxyinosine, guanosine, deoxyguanosine, and the nucleoside analogs 2',3'-dideoxyinosine and 8-azaguanosine are substrates, while adenosine and deoxyadenosine are not. IMP, deoxyIMP, GMP, and deoxyGMP are the best phosphate donors. The cytosolic 5'-nucleotidase/phosphotransferase substrate, 8-azaguanosine, was found to be very toxic for cultured fibroblasts (LD50 = 0.32 microM). Mutants resistant to either 8-azaguanosine and the correspondent base 8-azaguanine were isolated and characterized. Our results indicated that the 8-azaguanosine-resistant cells were lacking both cytosolic 5'-nucleotidase and hypoxanthine-guanine phosphoribosyltransferase, while 8-azaguanine resistant cells were lacking only the latter enzyme. Despite this observation, both mutants displayed 8-azaguanosine resistance, thus indicating that cytosolic 5'-nucleotidase is not essential for the activation of this nucleoside analog.
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