Purine nucleoside phosphorylase (PNP) catalyzes the reversible phosphorolysis of purine ribonucleosides and 2′-deoxypurine ribonucleosides to the free base, and ribose 1-phosphate or 2′-deoxyribose 1-phosphate, respectively.1–3 PNPs are found in most prokaryotic and eukaryotic organisms where the en...