ARG--TYR--LEU--PRO-THR

Proctolin can increase the frequency of action potentials, increase the amplitude of muscle contraction, and initiate activity in quiescent systems. In the arthropods, Proctolin acts as a neuromodulator and possibly as a neurohormone. It does not appear to function as a conventional neurotransmitter. Proctolin is a pentapeptide with the mature peptide of RYLPT, and it is the first insect neuropeptide to be sequenced and chemically characterized. The first identification of a Proctolin precursor gene is CG7105 in D. melanogaster . Although a previous study showed that Proctolin is absent in B. mori , this pentapeptide is recently identified in a proteomic analysis of B. mori wings. However, the Bombyx Proctolin gene does not produce a mature peptide because cleavage sites are not present at the N-terminal and C-terminal of the RYLPT sequence, and a similar gene is observed in C. suppressalis . Therefore, a true Proctolin has been considered to be not observed in B. mori and C. suppressalis .