Two peptides were purified from intestinal extracts of a sea cucumber, Holothuria glaberrima, by high pressure liquid chromatography (HPLC). The peptides were detected by a radioimmunoassay (RIA) based on an antiserum raised to the molluscan peptide, pGlu-Asp-Pro-Phe-Leu-Arg-Phe-NH2 (pQDPFLRFamide). Automated sequencing and mass spectrometry indicate that the isolated peptides are: Gly-Phe-Ser-Lys-Leu-Tyr-Phe-NH2 (GFSKLYFamide) and Ser-Gly-Tyr-Ser-Val-Leu-Tyr-Phe-NH2 (SGYSVLYFamide). These are the first peptides to have been isolated from a member of the echinoderm class Holothuroidea. The antiserum used in the RIA of the peptides was also employed in localizing immunoreactive nerve cells and fibers in the intestine of H. glaberrima. The immunohistochemical results suggest that these peptides might be responsible for the FMRFamide-like immunoreactivity reported earlier. Sequence similarities between GFSKLYFamide, SGYSVLYFamide, and a pair of peptides previously isolated from starfish lead us to propose that all four molecules are members of a family of peptides acting as neurotransmitters in echinoderms.

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