Human Phosphoribosylpyrophosphate (PRPP) Synthetase Requirements for Subunit Aggregation

The high energy sugar phosphate 5-phosphoribosyl 1-pyrophosphate (PRPP) is synthesized from MgATP and ribose-5-phosphate in a reaction catalyzed by PRPP synthetase (E.C. 2.7.6.1). In vitro studies of this enzyme,1–6 as well as evaluations of PRPP production in intact cells, 7,8 indicate that PRPP synthetase activity is regulated in a complex fashion involving the interaction of substrates, activators, reaction products and diverse inhibitors. Enzyme activity is strictly dependent upon the presence of inorganic phosphate (Pi) and Mg2+ which serve both as activators and cofactors.3 Among inhibitors of PRPP synthetase activity are purine, pyrimidine and pyridine nucleotide end-products of the pathways of PRPP utilization, the reaction products (PRPP and AMP), and 2,3-DPG.3,6