Isolation and characterization of the intestinal peptide porcine PHI (PHI-27), a new member of the glucagon--secretin family.

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Abstract
A new peptide, designated PHI (PHI-27), was discovered and isolated from porcine upper intestinal tissue by using a chemical method for finding peptide hormones and other active peptides. The method is based on chemical detection of peptides having the COOH-terminal .alpha.-amide structure, which is an unusual chemical feature of some peptide hormones and active peptides. Porcine PHI was found in the intestinal extract by the presence of its COOH-terminal isoleucine amide structure. It consists of 27 amino acid residues and has the following amino acid sequence: His-Ala-Asp-Gly-Val-Phe-Thr-Ser-Asp-Phe-Ser-Arg-Leu-Leu-Gly-Gln-Leu-Ser-Ala-Lys-Lys-Tyr-Leu-Glu-Ser-Leu-Ile-NH2. The remarkable sequence homology of PHI to vasoactive intestinal peptide, secretin, glucagon and gastric inhibitory polypeptide indicates that this peptide is a membrane of the glucagon-secretin family. Several biological activities of PHI, similar to those of vasoactive intestinal peptide and secretin, were reported.