The partial structure of a polypeptide with inhibitory activity for gastric secretion has been found to be Tyr-(Ala2, Asx, Glx, Gly, Ile2, Phe, Ser2, Thr, Tyr)-Met-Asp-Lys-Ile-Arg-Gln-(Ala, Asx2, Glx2-3, Leu, Phe, Val, Trp)-Lys-Gly-Lys-Lys-Ser-Asp-Trp-Lys-His-(Asx, Ile, Thr, Gln).
Tyr-(Ala2, Asx, Glx, Gly, Ile2, Phe, Ser2, Thr, Tyr)-Met-Asp-Lys-Ile-Arg-Gln-(Ala, Asx2, Glx2-3, Leu, Phe, Val, Trp)-Lys-Gly-Lys-Lys-Ser-Asp-Trp-Lys-His-(Asx, Ile, Thr, Gln).