Characterization of Two Novel Neuropeptides From the Sea Cucumber Holothuria glaberrima

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Abstract
Two peptides were purified from intestinal extracts of a sea cucumber, Holothuria glaberrima, by high pressure liquid chromatography (HPLC). The pep- tides 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 echi- noderm 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 immunohis- tochemical results suggest that these peptides might be responsible for the FMRFamide-like immunoreactivity reported earlier. Sequence similarities between GFSIUYFamide, SGYSVLYFamide, and a pair of pep tides 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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