Cecropin P1 (SWLSKTAKKLENSAKKRISEGIAIAIQGGPR), a homolog of insect cecropins isolated from pig intestine, was thought to be the first mammalian antimicrobial peptide. Later studies showed that the peptide is produced by the intestinal parasitic nematode Ascaris suum. The 31 amino acid peptide is highly potent against Gram-negative bacteria but has a reduced activity against Gram-positive bacteria. A disruptive effect on bacterial membranes has been proposed as mechanism of antimicrobial activity.
E.Gazit et al., Biochemistry, 34, 11479 (1995) J.-Y.Lee, Proc. Natl. Acad. Sci. USA, 86, 9159 (1989)