Proctolin needs to be broken down to stop it staying permanently bound to the receptor. This is done by peptidases. The first step of breakdown is cleavage of the Arg-Tyr bond, followed by the cleavage of the Tyr-Leu bond. Using a number of tissue homogenates from Periplaneta americana a soluble aminopeptidase as a key enzyme that degrades proctolin was identified. Another enzyme was also identified that cleaves the Tyr-Leu bond.
