Cyclic nucleotide phosphodiesterase with a dual specificity for the second messengers cAMP and cGMP, which are key regulators of many important physiological processes. Has a preference for cGMP as a substrate. a nucleoside 3',5'-cyclic phosphate + H2O = a nucleoside 5'-phosphate + H(+) 3',5'-cyclic GMP + H2O = GMP + H(+) 3',5'-cyclic AMP + H2O = AMP + H(+) Binds 2 divalent metal cations per subunit. Site 1 may preferentially bind zinc ions. Binds 2 divalent metal cations per subunit. Site 2 has a preference for magnesium ions. Type I PDE are activated by the binding of calmodulin in the presence of Ca(2+). Homodimer. Expressed in central nervous system regions. Most abundant in basal ganglia. Also found in kidney papilla and adrenal medulla. Belongs to the cyclic nucleotide phosphodiesterase family. PDE1 subfamily.