Nucleotidase that preferentially dephosphorylates 5'-GMP and 5'-AMP. a ribonucleoside 5'-phosphate + H2O = a ribonucleoside + phosphate Binds 1 Mg(2+) ion per subunit. In contrast to other surE homologs, is essentially inactive with other divalent cations. Inhibited by vanadate and tungstate. Optimum pH is 5.5-6.2. Optimum temperature is 80 degrees Celsius. Active up to 95 degrees Celsius. Homodimer and possibly homotetramer. Belongs to the SurE nucleotidase family. Was originally annotated as an acid phosphatase (EC 3.1.3.2).