Proctolin

Proctolin is a peptide neurotransmitter in insects and crustaceans. It has the amino acid sequence COOH-Arg-Tyr-Leu-Pro-Thr-NH2. Proctolin was originally isolated as "gut-factor" from the cockroach Periplaneta americana and was the first insect peptide to be characterised. Proctolin's presence was demonstrated in neurons of a number of arthropods. In motorneurons, it is thought to act as a co-transmitter that is secreted together with fast-acting neurotransmitters such as glutamate.