Final answer:
Cyclic AMP phosphodiesterase terminates a cyclic AMP-mediated response by converting cyclic AMP to AMP, thus halting the signaling pathway initially activated by cyclic AMP.
Step-by-step explanation:
The enzyme cyclic AMP phosphodiesterase terminates a response mediated by an increase in cyclic AMP by converting cyclic AMP to AMP. This enzyme catalyzes the breakdown of cyclic AMP, thus reducing its concentration in the cell and effectively stopping the signaling pathways originally activated by its increase. It is important to note that cyclic AMP acts as a second messenger within the cell, so when its levels decrease due to the action of the phosphodiesterase, the cascade of cellular responses that was initiated by the increase in cyclic AMP is halted.