Evolution of a Molluscan Cardioregulatory Neuropeptide

SYNOPSIS. The cardioexcitatory neuropeptide FMRFamide was firstidentified from a clam, but has now been demonstrated in severalother molluscs. It is probably present throughout the molluscanphylum though co-existing with related peptides in some species.For example, I report here the finding of the peptide phenylalanyl-leucyl-arginyl-phenylalanineamide (FLRFamide) in the mesogastropod Pomacea paludosa whereit accounts for 10–20% of the total FMRFamide-like activity.This peptide may be a minor component of the FMRFamide-likeactivity in other species as well. The pulmonate snails haveseveral, closely-related, heptapeptide analogs of FLRFamidethat are unique to them, such as pyroglutamyl-aspartyl-prolyl-phenylalanyl-leucyl-arginyl-phenylalanineamide (pQDPFLRFamide) which was isolated from Helix aspersa.Two additional pulmonate heptapeptides that have been isolatedprobably differ from pQDPFLRFamide only in their N-terminalamino acid residues. The heptapeptides account for most of theFMRFamidelike activity in the species in which they occur. Though the tetrapeptides FMRFamide and FLRFamide have virtuallyidentical activities on various molluscan tissues, the heptapeptideshave activity that is distinct from the tetrapeptides on somepulmonate muscles. 1 have attempted to explain the evolutionof this diversity of peptide structure and function found inthe modern pulmonates by postulating a gene duplication in thegastropod line leading to them.