Eight novel FMRFamide-like neuropeptides isolated from the nematode Ascaris suum.

Eight FMRFamide-like neuropeptides were isolated from an extract of heads and tails from the nematode Ascaris suum using seven steps of HPLC. The peptides ranged in size from 8 to 14 amino acid residues: AF3 (Ala-Val-Pro-Gly-Val-Leu-Arg-Phe-amide), AF4 (Gly-Asp-Val-Pro-Gly-Val-Leu-Arg-Phe-amide), AF5 (Ser-Gly-Lys-Pro-Thr-Phe-Ile-Arg-Phe-amide), AF7 (Ala-Gly-Pro-Arg-Phe-Ile-Arg-Phe-amide), AF9 (Gly-Leu-Gly-Pro-Arg-Pro-Leu-Arg-Phe-amide), AF10 (Gly-Phe-Gly-Asp-Glu-Met-Ser-Met-Pro-Gly-Val-Leu-Arg-Phe-amide), AF11 (Ser-Asp-Ile-Gly-Ile-Ser-Glu-Pro-Asn-Phe-Leu-Arg-Phe-amide), and AF12 (Phe-Gly-Asp-Glu-Met-Ser-Met-Pro-Gly-Val-Leu-Arg-Phe-amide). The effect of synthetic AF4 on muscle tension in a dorsal muscle strip preparation was a strong, long-lasting contraction. PF1, a peptide present in Panagrellus redivivus and Caenorhabditis elegans, relaxed the AF4-induced contraction.