2 S-IAMIDE PEPTIDES, AKSGFVRIAMIDE AND VSSFVRIAMIDE, ISOLATED FROM ANANNELID, PERINEREIS-VANCAURICA

Two peptides, H-Ala-Lys-Ser-Gly-Phe-Val-Arg-Ile-NH2 (AKSGFVRIamide), a nd 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 invol ved in the regulation of gut motility of the animal. The sequences of these peptides are very similar to those of other S-Iamide family pept ides which have been previously isolated from an echiuroid worm and so me molluscs. In particular, the sequence of VSSFVRIamide is identical to that of an echiuroid S-Iamide peptide. All of the molluscan and ech iuroid S-Iamide peptides, as well as the annelid peptides, were found to produce contractions in the esophagus of Perinereis. On the other h and, the annelid S-Iamide peptides, as well as the molluscan and echiu roid peptides, were found to inhibit or potentiate contractions elicit ed by electrical stimulation in echiuroid and molluscan muscles. S-Iam ide peptides may be a typical neuropeptide family distributed interphy letically in the Protostomia.