ISOLATION OF 3 ANTIBACTERIAL PEPTIDES FROM PIG INTESTINE - GASTRIC-INHIBITORY POLYPEPTIDE(7-42), DIAZEPAM-BINDING INHIBITOR(32-86) AND A NOVEL FACTOR, PEPTIDE-3910

Two antibacterial peptides, cecropin P1 and PR-39 (39-residue proline/ arginine-rich peptide), from the upper part of pig small intestine hav e previously been isolated and characterized. We have now continued ou r search for antibacterial peptides in different side fractions genera ted during the isolation of intestinal hormones. Starting from one suc h fraction and monitoring activity against Bacillus megaterium, we iso lated three homogeneous peptides by three consecutive chromatographic steps. Amino acid sequence analysis in combination with mass spectrome try identified two of the peptides as gastric inhibitory polypeptide(7 -42) [GIP(7-42)] and diazepam-binding inhibitor(32-86) [DBI(32-86)], d erived from factors already known. However, intact GIP and DBI have ha rdly any antibacterial activity by themselves. The third peptide const itutes a previously unknown structure, designated as peptide 3910 from its molecular mass. All three peptides showed good activity against B . megaterium. In addition, GIP(7-42) showed some activity against Stre ptococcus pyogenes and an Escherichia coli mutant with a defect in its outer membrane.