Potent bactericidal activity of bovine lactoferrin hydrolysate produced by heat treatment at acidic pH

A hydrolysate of bovine lactoferrin produced by heat treatment under acidic conditions had antibacterial activity at concentrations of 10 micrograms/ml in the culture medium. The optimal degree of hydrolysis for this activity was about 10%. Heat-treated lactoferrin, treated at pH 2.0 and 120 degrees C for 15 min and degree of hydrolysis of about 10%, had no Fe-binding capacity (0%) and less antigenicity (about 10(-6) than untreated lactoferrin. Heat-treated lactoferrin increased in antibacterial activity, and the activity was maintained in an Fe-rich medium. After fractionation of heat-treated lactoferrin by reverse-phase HPLC, several peptide fractions were found that had strong antibacterial activity. It was suggested that lactoferrin latently contains at least one bactericidal domain that is activated upon release by limited acid hydrolysis of the protein. The bactericidal activity of the peptide fragments of lactoferrin was shown to have no relation to Fe chelation, in contrast with the antibacterial mechanism of native lactoferrin.