Primary structure of ovine hypothalamic somatostatin-28 and somatostatin-25.

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Abstract
The primary structure of the NH2-terminally extended somatostatins isolated from ovine hypothalamic extracts, one containing 28 residues and the other 25, was determined. The structure of somatostatin-28 is Ser-Ala-Asn-Ser-Asn-Pro-Ala-Met-Ala-Pro-Arg-Glu-Arg-Lys-Ala-Gly- .**GRAPHIC**. the shorter one, somatostatin-25, has the same sequence as somatostatin-28 except that the first 3 NH2-terminal residues are deleted. The 2 peptides as isolated were oxidized at the methionine residue to the methionine sulfoxide. Their structures were established by subjecting the native peptides to direct sequence analysis in a Beckman 890C sequencer and identifying the released phenylthiohydantoin derivatives by high-performance liquid chromatography [HPLC]. Their structures were confirmed by trypsin digestion and isolation of all the tryptic peptides, followed by amino acid analysis of the tryptic fragments. Moreover, some of the tryptic peptides were matched with their respective synthetic replicates on HPLC.