Purine-nucleoside Phosphorylase

In enzymology, a purine-nucleoside phosphorylase (EC 2.4.2.1) is an enzyme that catalyzes the chemical reaction

purine nucleoside + phosphate purine + alpha-D-ribose 1-phosphate

Thus, the two substrates of this enzyme are purine nucleoside and phosphate, whereas its two products are purine and alpha-D-ribose 1-phosphate.

This enzyme belongs to the family of glycosyltransferases, specifically the pentosyltransferases. The systematic name of this enzyme class is purine-nucleoside:phosphate ribosyltransferase. Other names in common use include inosine phosphorylase, PNPase, PUNPI, PUNPII, inosine-guanosine phosphorylase, nucleotide phosphatase, purine deoxynucleoside phosphorylase, purine deoxyribonucleoside phosphorylase, purine nucleoside phosphorylase, and purine ribonucleoside phosphorylase. This enzyme participates in 3 metabolic pathways: purine metabolism, pyrimidine metabolism, and nicotinate and nicotinamide metabolism.