Three cysteine-rich cationic peptides, designated RatNP-1, RatNP-3, and RatNP-4, were purified from an acid extract of rat polymorphonuclear neutrophils, sequenced, and tested for antimicrobial activity. The peptides ranged from 29 to 32 amino acids in length (Mr, 3,252 to 3,825), and each contained all eight invariantly conserved "framework" residues that are characteristic of defensins. Each of the peptides killed Escherichia coli ML-35, Acinetobacter calcoaceticus HON-1, Staphylococcus aureus 502A, and Candida albicans 820 in vitro. RatNP-1, the most cationic rat defensin, was also the most potent. With this report, a total of 13 distinct defensins have been characterized in the polymorphonuclear leukocytes of four mammalian species. The existence of the defensin system in rats should facilitate investigations of the in vivo role of defensins in experimental infections.
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