The ubiquitous intracellular second messengers 3′,5′-cyclic adenosine monophosphate (cAMP) and 3′,5′-cyclic guanosine monophosphate (cGMP) mediate the effects of a large variety of hormones and neurotransmitters. Both of these nucleotides are inactivated by a large group of enzymes collectively known as 3′,5′-cyclic nucleotide phosphodiesterases (PDEs; EC 3.1.4.17), which catalyze the hydrolytic cleavage of the 3′ phosphodiesterase bond to form the corresponding 5′ nucleotide (i.e., 5′AMP or 5′GMP; Fig. 1 ). Fig. 1. The hydrolytic reaction catalyzed by 3′,5′-cyclic nucleotide phosphodiesterases.
