Answer:
The correct option is the degradation of the transmitter molecules by enzymes.
Explanation:
The key lock system is a type of enzymatic catalysis / anabolization, and is so called because the enzyme that reacts with its substrate is in the male-female or key lock format.
Enzymes can also react by other mechanisms, but this is known for the perfect fit of the substrate with the binding site, since one represents the negative of the other, once joined and the reaction started, the active site is occupied and the enzyme is not reacts with another substrate simultaneously to that one.