purine-nucleoside phosphorylase

pur·ine-nu·cle·o·side phos·phor·y·lase

a ribosyltransferase that reversibly catalyzes the phosphorolysis of a purine nucleoside with orthophosphate to produce a purine and α-d-ribose 1-phosphate; an inherited deficiency of this enzyme leads to cellular immunodeficiency.