Somatostatin-related and glucagon-related peptides with unusual structural features from the European eel (Anguilla anguilla)

Peptides derived from prosomatostatins I and II and from two distinct proglucagons have been isolated from the pancreas of a teleost fish, the European eel (Anguilla anguilla). The product of prosomatostatin I processing, somatostatin-14, is identical to mammalian somatostatin-14. A 25-amino-acid-residue peptide (Ser-Val-Asp-Asn-Gln⁵-Gln- Gly-Arg-Gly-Arg¹⁰-Lys-Ala-Gly-Cys-Lys¹⁵-Asn-Phe-Tyr-Trp-Lys²⁰-Gly-Pro- Thr-Ser-Cys²⁵) is derived from prosomatostatin II. Compared with the corresponding peptides from other teleost fish, the eel somatostatin-25 contains the unusual substitution Pro for Phe at position 22. This peptide was also isolated in a form containing a hydroxylysyl residue at position 20. A 29-amino-acid-residue eel glucagon contains four substitutions relative to human glucagon Asn for Ser⁸, Glu for Asp¹⁵, Thr for Ser¹⁶, and Ser for Thr²⁹). In common with mammalian and avian glucagons but unlike most other fish glucagons, the eel peptide possesses a glutamine residue at position 3. A peptide derived from a second proglucagon comprises 36 amino acid residues. A 7-residue C-terminal extension to the glucagon sequence shows structural similarity to the corresponding extension in ratfish (Hydrolagus colliei) glucagon and mammalian oxyntomodulin.