 Increased hydrolysis of cAMP due to binding of cGMP to the GAF-B domain is well documented, however there are no known examples for the reverse.It has been shown that the GAF-B domain has 30-100 fold lower affinity for cAMP than for cGMP.This information combined with what is currently known about intracellular cAMP concentrations, renders it unlikely that activation of cGMP hydrolysis by cAMP can take place in vivo.