Isolation and characterization of a novel myoactive tetradecapeptide-related peptide isolated from the brain of the squid, Todarodes pacificus

A new bioactive tetradecapeptide, GFKDNVSNRIAHGFamide, was isolated from the brain of the squid, Todarodes pacificus. Using isolated T. pacificus esophagus as a bioassay, the peptide was shown to induce potent contraction of smooth muscle. The threshold concentration for contraction was 5 × 10⁻¹⁰ M to 1 × 10⁻⁹ M. The peptide was homologous to other molluskan (class Gastropoda) and annelid myoactive tetradecapeptides and to some extent, to arthropodan tridecapeptides. A full-length cDNA encoding the biosynthetic precursor of the active peptide was cloned, revealing that the peptide is probably secreted following processing of a prepropeptide containing a signal peptide and prosequences. This is the first myoactive tetradecapeptide (MATP) to be isolated from any mollusk of the class Cephalopoda and we have named it Todarodes tetradecapeptide (TTP).