Purine salvage pathway enzyme that catalyzes the transfer of the ribosyl-5-phosphate group from 5-phospho-alpha-D-ribose 1-diphosphate (PRPP) to the N9 position of the 6-oxopurines hypoxanthine and guanine to form the corresponding ribonucleotides IMP (inosine 5'-monophosphate) and GMP (guanosine 5'-monophosphate), with the release of PPi (PubMed:19362594, PubMed:25915781). Thus, specifically recycles hypoxanthine and guanine imported from the external medium, and converts them to IMP and GMP, respectively. Cannot use xanthine as substrate (PubMed:19362594). diphosphate + IMP = 5-phospho-alpha-D-ribose 1-diphosphate + hypoxanthine diphosphate + GMP = 5-phospho-alpha-D-ribose 1-diphosphate + guanine Competitively inhibited by acyclic nucleoside phosphonates (ANPs) with Ki values as low as 0.69 uM. Prodrugs of these compounds arrest the growth of a virulent strain of M.tuberculosis with MIC50 values as low as 4.5 uM and possess low cytotoxicity in mammalian cells (PubMed:25915781). Inhibited by pyrrolidine nucleoside bisphosphonates, which are also able to arrest the growth of virulent M.tuberculosis not only in its replicating phase but also in its latent phase, and to arrest the growth of M.tuberculosis in infected macrophages while having low cytotoxicity in mammalian cells (PubMed:30265958). kcat is 0.14 sec(-1) with guanine as substrate. kcat is 0.9 sec(-1) with hypoxanthine as substrate (at pH 7.4 and 25 degrees Celsius) (PubMed:19362594). kcat is 0.62 sec(-1) with guanine as substrate. kcat is 0.55 sec(-1) with hypoxanthine as substrate (at pH 7.4 and 25 degrees Celsius) (PubMed:25915781). Purine metabolism; IMP biosynthesis via salvage pathway; IMP from hypoxanthine: step 1/1. Purine metabolism; GMP biosynthesis via salvage pathway; GMP from guanine: step 1/1. Homodimer and homotetramer in equilibrium. The presence or absence of divalent metal ions, as well as phosphate, can affect the oligomerization state of the enzyme. Likely functions as a tetramer (rather than a dimer) in its biological environment, which is the most active form. The dimeric structure is also active though ~50% of that of the tetramer. Is a target for anti-TB drug development. Belongs to the purine/pyrimidine phosphoribosyltransferase family. Extended N-terminus.