In enzymology, a purine nucleosidase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are purine nucleoside and H<sub>2</sub>O, whereas its two products are D-ribose and purine base.
This enzyme belongs to the family of hydrolases, specifically those glycosylases that hydrolyse N-glycosyl compounds. The systematic name of this enzyme class is purine-nucleoside ribohydrolase. Other names in common use include nucleosidase, purine beta-ribosidase, purine nucleoside hydrolase, purine ribonucleosidase, ribonucleoside hydrolase, nucleoside hydrolase, N-ribosyl purine ribohydrolase, nucleosidase g, N-D-ribosylpurine ribohydrolase, inosine-adenosine-guanosine preferring nucleoside hydrolase, purine-specific nucleoside N-ribohydrolase, IAG-nucleoside hydrolase, and IAG-NH. This enzyme participates in purine metabolism and nicotinate and nicotinamide metabolism.
As of late 2007, 11 structures have been solved for this class of enzymes, with PDB accession codes , , , , , , , , , , and .