Phosphodiesterase-5 (<< PDE5 >>) contains a catalytic domain (C domain) that hydrolyzes [[ cGMP ]] and a regulatory domain (R domain) that contains two mammalian cGMP-binding phosphodiesterase, Anabaena adenylyl cyclases, Escherichia coli FhlAs (GAFs) (A and B) and a phosphorylation site for cyclic nucleotide-dependent protein kinases (cNPKs).