Cytosolic 5'-nucleotidase IA catalyzes the hydrolysis of purine ribo- and deoxyribonucleoside monophosphates to nucleosides plus orthophosphate. The enzyme is allosterically activated by ADP (Hunsucker et al. 2001). The human enzyme is inferred to be a homotetramer with one Mg++ ion bound per subunit, based on its similarity to the pigeon heart enzyme (Bianchi and Spychala 2003; Sala-Newby et al. 1999; Skladanowski and Newby 1990).