PRPP synthetase is an enzyme that catalyzes there reaction below (see here also):

ATP + Ribose-5-Phosphate <=> PRPP + AMP

PRPP is an important intermediate in the de novo synthesis of purines pathway (Figure 22.4). Defects in PRPP synthetase may render it insensitive to feedback inhibition by purine nucleotides. Thus, purine nucleotides are overproduced, leading to excessive uric acid synthesis and gout (Figure 22.9).