Final answer:
Phosphodiesterase (PDE) is the substrate for cyclic AMP (cAMP), while adenosine monophosphate (AMP) is the product.
Step-by-step explanation:
Phosphodiesterase (PDE) is a cytosolic enzyme that degrades cyclic AMP (cAMP) in cells. It removes the phosphate group from cAMP, converting it into adenosine monophosphate (AMP) and terminating the signaling cascade. In this process, PDE acts as the substrate for cAMP, while AMP is the product formed.