The purine nucleoside phosphorylases catalyze 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. Cleaves guanosine, inosine, 2'-deoxyguanosine and 2'-deoxyinosine. a purine D-ribonucleoside + phosphate = a purine nucleobase + alpha-D-ribose 1-phosphate a purine 2'-deoxy-D-ribonucleoside + phosphate = 2-deoxy-alpha-D-ribose 1-phosphate + a purine nucleobase Purine metabolism; purine nucleoside salvage. Homotrimer. Belongs to the PNP/MTAP phosphorylase family.