Purine and pyrimidine salvage in whole rat brain. Utilization of ATP-derived ribose-1-phosphate and 5-phosphoribosyl-1-pyrophosphate generated in experiments with dialyzed cell-free extracts.
The object of this work stems from our previous studies on the mechanisms responsible of ribose-1-phosphate- and 5-phosphoribosyl-1-pyrophosphate-mediated nucleobase salvage and 5-fluorouracil activation in rat brain (Mascia, L., Cappiello M., Cherri, S., and Ipata, P. L. (2000) Biochim. Biophys. Acta 1474, 70-74; Mascia, L., Cotrufo, T., Cappiello, M., and Ipata, P. L. (1999) Biochim. Biophys. Acta 1472, 93-98). Here we show that when ATP at "physiological concentration" is added to dialyzed extracts of rat brain in the presence of natural nucleobases or 5-fluorouracil, adenine-, hypoxanthine-, guanine-, uracil-, and 5-fluorouracil-ribonucleotides are synthesized. The molecular mechanism of this peculiar nucleotide synthesis relies on the capacity of rat brain to salvage purine and pyrimidine bases by deriving ribose-1-phosphate and 5-phosphoribosyl-1-pyrophosphate from ATP even in the absence of added pentose or pentose phosphates. The levels of the two sugar phosphates formed are compatible with those of synthesized nucleotides. We propose that the ATP-mediated 5-phosphoribosyl-1-pyrophosphate synthesis occurs through the action of purine nucleoside phosphorylase, phosphopentomutase, and 5-phosphoribosyl-1-pyrophosphate synthetase. Furthering our previous observations on the effect of ATP in the 5-phosphoribosyl-1-pyrophosphate-mediated 5-fluorouracil activation in rat liver (Mascia, L., and Ipata, P. L. (2001) Biochem. Pharmacol. 62, 213-218), we now show that the ratio [5-phosphoribosyl-1-pyrophosphate]/[ATP] plays a major role in modulating adenine salvage in rat brain. On the basis of our in vitro results, we suggest that massive ATP degradation, as it occurs in brain during ischemia, might lead to an increase of the intracellular 5-phosphoribosyl-1-pyrophosphate and ribose-1-phosphate pools, to be utilized for nucleotide resynthesis during reperfusion.
Barsotti
Catia
C
Department of Physiology and Biochemistry, University of Pisa, Via Santa Maria 55, 56126 Pisa, Italy.
Tozzi
Maria G
MG
Ipata
Piero L
PL
D000225:Adenine / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002474:Cell-Free System; D003596:Cytosine / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D019271:Hypoxanthine / Q000378:metabolism; D007511:Ischemia; D008956:Models, Chemical; D010429:Pentoses / Q000378:metabolism; D010754:Phosphoribosyl Pyrophosphate / Q000737:chemistry / Q000378:metabolism*; D011687:Purines / Q000737:chemistry* / Q000378:metabolism; D011743:Pyrimidines / Q000737:chemistry* / Q000378:metabolism; D051381:Rats; D015427:Reperfusion Injury; D012267:Ribosemonophosphates / Q000737:chemistry / Q000378:metabolism*; D013997:Time Factors
D010429:Pentoses; D011687:Purines; D011743:Pyrimidines; D012267:Ribosemonophosphates; C031154:ribose 1-phosphate; D019271:Hypoxanthine; D010754:Phosphoribosyl Pyrophosphate; D003596:Cytosine; D000255:Adenosine Triphosphate; D000225:Adenine