Coelenterate Neuropeptides: Structure, Action and Biosynthesis

Evolutionary “old” nervous systems such as those of coelenterates are peptidergic: Using various radioimmunoassays we have now isolated 13 novel neuropeptides from sea anemones and several others from hydrozoan polyps and medusae. These peptides are all structurally related and contain the C-terminal sequence Arg-X-NH2 or Lys-X-NH2, where X is Ala, Asn, Ile, Phe, Pro or Trp. Three neuropeptides have a novel N-terminal L-3-phenyllactyl residue, which protects against degradation by nonspecific aminopeptidases. The neuropeptides from sea anemones are produced by different sets of neurones and have excitatory or inhibitory actions on isolated muscle preparations, suggesting that they are neurotransmitters or neuromodulators. We have also cloned the precursor protein for the sea-anemone neuropeptide Antho-RFamide (