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A 31-amino acid synthetic peptide (NH(2)-FFSASCVPGADKGQFPNLCRLCAGTGENKCA-COOH) was chemically synthesized based on the amino acid sequence of a region of human lactoferrin homologous to other sequences present in the N- and C-lobes of all members of the transferrin family proteins. The peptide, termed kaliocin-1, and lactoferrin showed a bactericidal effect in assays performed in low-ionic-strength conditions. This is the first time that it is shown that the antimicrobial effect of lactoferrin depends on the extracellular cation concentration. The antimicrobial effect of kaliocin-1 was lower than that of human lactoferrin, but their activities were inhibited by Na(+) or K(+) in a cation concentration-dependent manner. In addition, the peptide was able to mimic native lactoferrin, inducing K(+)-efflux and a selective dissipation of the transmembrane electrical potential of Escherichia coli cells without causing extensive damage to the outer and inner bacterial membranes. In contrast, the peptide, but not lactoferrin, was able to permeabilize different ions through liposomal membranes. The hypothetical interaction of kaliocin-1 with a bacterial membrane compound is discussed based in the different ion flux induced on cellular and artificial membranes as well as data from circular dichroism assays. Kaliocin-1 was not cytotoxic and could be a suitable model for the design of analogs able to mimic the antibacterial effect of human lactoferrin.