Synthesis of (14C)-Ribose-5-Phosphate and (14C)-Phosphoribosyl-Pyrophosphate and Their use in New Enzyme Assays
Phosphoribosylpyrophosphate (PP-ribose-P) is a specific substrate for eight synthetic enzymes in mammalian cells (1). Three of these enzymes, glutamine phosphoribosylpyrophosphate amidotrans-ferase (PP-ribose-P amidotransferase, (EC.18.104.22.168), hypoxanthine-guanine phosphoribosyltransferase (HPRT, EC.22.214.171.124) and adenine phosphoribosyltransferase (APRT, EC.126.96.36.199) are required for purine nucleotide synthesis and one, orotate phosphoribosyltransferase (OPRT, EC.188.8.131.52) for pyrimidine nucleotide synthesis. Since PP-ribose-P serves not only as a substrate of PP-ribose-P amido-transferase, but also as an allosteric regulator of activity (2), the intracellular concentration of PP-ribose-P appears to be a major determinant of purine nucleotide synthesis. The immediate precursor of PP-ribose-P is ribose-5-phosphate (ribose-5-P).
KeywordsSynthetase Activity Purine Metabolism Allosteric Regulator Nucleotide Synthesis Synthetic Enzyme
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