Purification and characterization of FMRFamidelike immunoreactive substances from the lobster nervous system: isolation and sequence analysis of two closely related peptides.

In the preceding paper (Kobierski et al: J. Comp. Neurol. 266:1-15, '87) FMRFamidelike immunoreactivity (FLI) was localized to specific cells and processes in the nervous system of the lobster Homarus americanus. In an effort to establish a role for this material we have purified and characterized a variety of immunoreactive peptides that can be extracted from the secretory pericardial organs. By using gel-filtration chromatography and three different HPLC systems, it has been established that little or no authentic FMRFamide is present. Of the major immunoreactive components two peptides were purified in sufficient quantity for microsequence analysis and have been tentatively identified as the octapeptides Ser-Asp-Arg-Asn-Phe-Leu-Arg-Phe-amide (FLI 3) and Thr-Asn-Arg-Asn-Phe-Leu-Arg-Phe-amide (FLI 4). Both of these are novel neuropeptides with some sequence homology to the previously described FMRFamide family. The pericardial organs release FLI when depolarized with 100 mM K+ in the presence of calcium. Between 75 and 80% of this release is accounted for by FLI 3 and FLI 4. One of these peptides (FLI 4) has been synthesized and shown to cochromatograph with the endogenous immunoreactive material. Preliminary studies show that this peptide can act as a modulator of exoskeletal and cardiac neuromuscular junctions.