Plays a role in signal transduction by regulating the intracellular concentration of cyclic nucleotides cAMP and cGMP (PubMed:10725373, PubMed:10906126, PubMed:11050148, PubMed:16330539). Catalyzes the hydrolysis of both cAMP and cGMP to 5'-AMP and 5'-GMP, respectively (PubMed:10725373, PubMed:10906126, PubMed:11050148). 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, while site 2 has a preference for magnesium and/or manganese ions. Inhibited by 3-isobutyl-1-methylxanthine (IBMX), zaprinast and dipyridamole. cGMP acts as an allosteric activator. Weakly inhibited by Sildenafil (Viagra) and Tadalafil (Cialis); however, the fact that the protein is probably absent from testis, suggests that it is not biologically relevant and is not related with erectile dysfunction. Isoform 1 is present in prostate, pituitary, heart and liver. It is however not present in testis nor in penis, suggesting that weak inhibition by Tadalafil (Cialis) is not relevant (at protein level). Isoform 2 may be expressed in testis. Isoform 4 is expressed in adrenal cortex. The tandem GAF domains bind cGMP, and regulate enzyme activity. The binding of cGMP stimulates enzyme activity. The disease is caused by variants affecting the gene represented in this entry. Belongs to the cyclic nucleotide phosphodiesterase family.