Amino acid sequence of catfish pancreatic somatostatin I.

Two peptides, pancreatic somatostatins I and II, larger and more acidic than synthetic tetradecapeptide somatostatin, have been purified from pancreatic islets of channel catfish (Ictalurus punctata). These peptides have reduced immunoreactivity in a radioimmunoassay for synthetic somatostatin, but full biological activity was measured as inhibition of growth hormone released from isolated rat anterior pituitary cells. Pancreatic somatostatin I is composed of 22 amino acids. Eight additional amino acids are found as an NH2-terminal extension of the segment which is homologous to synthetic tetradecapeptide somatostatin. Seven of fourteen residues of tetradecapeptide somatostatin are present in the COOH-terminal portion of catfish pancreatic somatostatin I. The sequence is NH2-Asp-Asn-Thr-Val-Arg-Ser-Lys-Pro-Leu-Asn-Cys-Met-Asn-Tyr-Phe-Trp-Lys-Ser-Ser-Thr-Ala-Cys-COOH. There is considerable homology with the carboxyl end of synthetic tetradecapeptide somatostatin.