[1] Proctolin was extracted from 125,000 cockroaches and the Edman degradation was carried out on the sample to determine the amino acid sequence, which is Arg-Tyr-Leu-Pro-Thr.

The preferred conformation of proctolin is a quasi-cyclic structure with the tyrosyl side chain pointing outwards.

This is because all proctolinergic systems change the way impulses are transmitted across a synapse, using proctolin as a cotransmitter, often with a more common neurotransmitter such as glutamate.

Proctolin stimulates contractions of the hindgut in P. americana, the foregut in S. gregaria and the midgut of Diploptera punctata and L. migratoria.

In Drosophila, this receptor is strongly expressed in the head, the larval hindgut, the aorta and on neuronal endings in adult hearts.

Using a number of tissue homogenates from Periplaneta americana a soluble aminopeptidase as a key enzyme that degrades proctolin was identified.