LymnaDFamides, a new family of neuropeptides from the pond snail, Lymnaea stagnalis. Clue to cholecystokinin immunoreactivity in invertebrates?

Five tridecapeptides have been identified from the central nervous system of the pond snail, Lymnaea stagnalis. The sequences are Pro-Xaa-Asp-Arg-Ile-Ser-Yaa-Ser-Ala-Phe-Ser-Asp-Phe. NH2, where Xaa is either Tyr or Phe and Yaa either Asn, Ser or Gly. The peptides are named lymnaDFamides to acknowledge identity with the C-terminal dipeptide of the mammalian neuropeptides, cholecystokinin (CCK) and gastrin. They were detected by an antiserum that recognizes the biologically active C-termini of cholecystokinin and gastrin. LymnaDFamide-1 (Xaa = Tyr and Yaa = Asn) had no effect on trout gallbladder, which responds equally to CCK and gastrin. We propose that the lymnaDFamides belong to an Asp-Phe-amide superfamily, which includes CCK and gastrin, and suggest that the widespread CCK/gastrin immunoreactivity in invertebrates is due to peptides belonging to such a superfamily.