The function of PNP (purine nucleoside phosphorylase, Ensembl gene identifier ENSG00000198805) is as follows. Catalyzes the phosphorolytic breakdown of the N-glycosidic bond in the beta-(deoxy)ribonucleoside molecules, with the formation of the corresponding free purine bases and pentose-1-phosphate (PubMed:23438750, PubMed:3029074, PubMed:9305964). Preferentially acts on 6-oxopurine nucleosides including inosine and guanosine (PubMed:9305964). {ECO:0000269|PubMed:23438750, ECO:0000269|PubMed:3029074, ECO:0000269|PubMed:9305964}.