Cytosolic purine 5'-nucleotidase (NT5C2) catalyzes the hydrolysis of GMP, dGMP, IMP, and dIMP to yield the corresponding nucleosides and orthophosphate (Bianchi and Spychala 2003; Spychala et al. 1988). The active form of the enzyme is a tetramer and has an absolute requirement for magnesium ions (Spychala et al. 1988; Wallden et al. 2007). Consistent with the biochemical properties of purified enzyme, cultured cells overexpressing the enzyme from a recombinant DNA clone showed enhanced activity against inosine and guanosine monophosphates, but not adenosine monophosphate (Gazziola et al. 2001; Sala-Newby et al. 2000).