Plays a role in signal transduction by regulating the intracellular concentration of cyclic nucleotides. This phosphodiesterase catalyzes the specific hydrolysis of cGMP to 5'-GMP. Specifically regulates nitric-oxide-generated cGMP. 3',5'-cyclic GMP + H2O = GMP + H(+) Binds 1 Zn(2+) ion per subunit. Binds 2 divalent metal cations per subunit: site 1 preferentially binds zinc, while site 2 has a preference for magnesium. Tightly binds zinc. Binds 1 Mg(2+) ions per subunit. Binds 2 divalent metal cations per subunit: site 1 preferentially binds zinc, while site 2 has a preference for magnesium. Binds magnesium less tightly than zinc. Purine metabolism; 3',5'-cyclic GMP degradation; GMP from 3',5'-cyclic GMP: step 1/1. Composed of a C-terminal catalytic domain containing two putative divalent metal sites and an N-terminal regulatory domain which contains two homologous allosteric cGMP-binding regions, A and B. Phosphorylation is regulated by binding of cGMP to the two allosteric sites. Phosphorylation by PRKG1 leads to its activation. Belongs to the cyclic nucleotide phosphodiesterase family.