Two S-Iamide Peptides, AKSGFVRIamide and VSSFVRIamide, Isolated from an Annelid, Perinereis vancaurica.

Two peptides, H-Ala-Lys-Ser-Gly-Phe-Val-Arg-Ile-NH2 (AKSGFVRIamide), and H-Val-Ser-Ser-Phe-Val-Arg-Ile-NH2 (VSSFVRIamide) were isolated from a polychaete annelid, Perinereis vancaurica. Both the peptides evoked rhythmic contractions in the esophagus of Perinereis with a threshold as low as 10-10-10-9 M, suggesting that the peptides may be involved in the regulation of gut motility of the animal. The sequences of these peptides are very similar to those of other S-Iamide family peptides which have been previously isolated from an echiuroid worm and some molluses. In particular, the sequence of VSSFVRIamide is identical to that of an echiuroid S-Iamide peptide. All of the molluscan and echiuroid S-Iamide peptides, as well as the annelid peptides, were found to produce contractions in the esophagus of Perinereis. On the other hand, the annelid S-Iamide peptides, as well as the molluscan and echiuroid peptides, were found to inhibit or potentiate contractions elicited by electrical stimulation in echiuroid and molluscan muscles. S-Iamide peptides may be a typical neuropeptide family distributed interphyletically in the Protostomia.