Purine Nucleoside Phosphorylase (PNP) (E.C. 2.4.2.1.) is an enzyme involved in purine metabolism and it catalyzes the cleavage of the glycosidic bond of ribo- or deoxyribonucleosides, in the presence of inorganic phosphate as a second substrate, to generate the purine base and ribose-1-phosphate or deoxyribose-1-phosphate. It is one of the enzymes of the nucleotide salvage pathways that allow the cell to produce nucleotide monophosphates when the de novo synthesis pathway has been interrupted or is non-existent (as is the case in the brain). PNP is a cytosolic enzyme. PNP deficiency disease leads to toxic buildup of deoxyguanosine in T-cells leading to T-lymphocytopenia with no apparent effects on B-lymphocyte function. Inhibition of PNP is an important target for chemotherapeutic applications and treatment of T-cell mediated autoimmune diseases. PNP deficiency is also associated with neurological problems. In Assay Genie's Purine Nucleoside Phosphorylase Activity Assay, hypoxanthine formed by the breakdown of inosine is further converted to uric acid using a developer. The uric acid is measured at a wavelength of 293 nm. Limit of quantification is 0.1 µU recombinant Purine Nucleoside Phosphorylase.

Figure: (a) Hypoxanthine Standard Curve, (b) Purine Nucleoside Phosphorylase Activity in Jurkat cell (T-lymphocyte) lysate (3 µg), rat brain lysate (19 µg), and positive Control (c) PNP specific activity in Jurkat cell lysate and rat brain lysate. Assays were performed following the kit protocol.