Purification, composition, and activity of two bactenecins, antibacterial peptides of bovine neutrophils

Abstract

Extracts of granules of bovine neutrophils are known to exhibit a marked antibacterial activity in vitro. By a simple, two-step chromatographic procedure, we have resolved two peptide components of the antibacterial system. They were named Bac-5 and Bac-7 from the general term bactenecin and had molecular masses of about 5 and 7 kilodaltons, respectively. Over 45 and 20% of the amino acid residues in the two bactenecins are proline and arginine, respectively. The remaining amino acids are mainly hydrophobic (isoleucine, leucine, and phenylalanine). Both Bac-5 and Bac-7 efficiently kill Escherichia coli, Salmonella typhimurium, and Klebsiella pneumoniae. They also arrest the growth of Enterobacter cloacae (MICs, 25 to 200 μg/ml) but of Proteus vulgaris, staphylococcus aureus, and streptococcus agalactiae (MIC, >200 μg/ml). Finally, Bac-7 but not Bac-5 has MICs of ≤200 μg/ml for Pseudomonas aeruginosa and Staphylococcus epidermidis. From the comparison between the efficient bactericidal concentrations in vitro and the estimated content of bactenecins in neutrophils (125 ng of Bac-5 and Bac-7 each per 106 cells), it is reasonable to conclude that the two cationic peptides may exert a major role in host defense against at least some microorganisms.