Cytosolic 5'-nucleotidase/nucleoside phosphotransferase: a nucleoside analog activating enzyme?
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.
Turriani
M
M
Dipartimento di Fisiologia e Biochimica, Università di Pisa, Italy.
Pesi
R
R
Nardone
A
A
Turchi
G
G
Sgarrella
F
F
Ipata
P L
PL
Tozzi
M G
MG
D015720:5'-Nucleotidase / Q000302:isolation & purification / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001375:Azaguanine / Q000378:metabolism / Q000633:toxicity*; D001711:Biotransformation; D002460:Cell Line; D002478:Cells, Cultured; D006224:Cricetinae; D003412:Cricetulus; D003600:Cytosol / Q000201:enzymology*; D004351:Drug Resistance; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D006151:Guanosine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000633:toxicity; D007041:Hypoxanthine Phosphoribosyltransferase / Q000378:metabolism; D007288:Inosine / Q000378:metabolism; D007291:Inosine Monophosphate / Q000378:metabolism; D008297:Male; D009154:Mutation; D010766:Phosphorylation; D010770:Phosphotransferases / Q000302:isolation & purification / Q000378:metabolism*
D006151:Guanosine; D007291:Inosine Monophosphate; C013405:azaguanosine; D007288:Inosine; D000255:Adenosine Triphosphate; D007041:Hypoxanthine Phosphoribosyltransferase; D010770:Phosphotransferases; C021892:nucleoside phosphotransferase; D015720:5'-Nucleotidase; D001375:Azaguanine