Isolation and structure of pro-somatostatin: a putative somatostatin precursor from pig hypothalamus.

An octacosapeptide that we named pro-somatostatin has been isolated from acid extracts of porcine hypothalami and found to have the amino acid sequence Ser-Ala-Asn-Ser-Asn-Pro-Ala-Met-Ala-Pro-Arg-Glu-Arg-Lys-Ala-Gly-Cys-Lys-Asn-Phe-Phe-Trp-Lys-Thr-Phe-Thr-Ser-Cys. This octacosapeptide possesses high somatotropin (growth hormone) and prolactin release-inhibiting activity in vitro. It also crossreacts strongly with antisera generated against the somatostatin tetradecapeptide. This octacosapeptide is most likely a precursor (pro-hormone) of somatostatin in the hypothalamus. The existence of still larger molecular size precursors of somatostatin was also observed.