What is "proctolin"

Proctolin is a neuropeptide present in insects and crustaceans. It was first found in Periplaneta americana, a species of cockroach in 1975. 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.

Proctolin was the first insect neuropeptide to be sequenced. Starratt and Brown identified it as a visceral muscle neurotransmitter. However, it now appears that there are many more functions of proctolin, and it is present in many more species.