Final answer:
Adenylyl cyclase produces cAMP, which targets and activates cAMP-dependent kinases, leading to the phosphorylation and activation of various proteins within the cell.
Step-by-step explanation:
Adenylyl cyclase catalyzes the conversion of ATP to cyclic AMP (cAMP), which is the secondary messenger in this pathway. The secondary messenger, cAMP, specifically targets and activates an enzyme known as cAMP-dependent kinase or A-kinase. A-kinase is vital in regulating metabolic pathways as it phosphorylates serine and threonine residues on target proteins, leading to their activation. Variations in target proteins among different cells give rise to a diversity of responses to cAMP in these cells.