Histatin 5 is a cationic salivary peptide with strong candidacidal and bactericidal activity at physiological concentration. In this paper we demonstrate by optical spectroscopy and ESI-IT-MS experiments that a synthetic peptide related to the N-terminus of histatin 5 specifically binds copper ions in vitro and that the complex metal-peptide generates reactive oxygen species at physiological concentration of ascorbate, leading to significant auto-oxidation of the peptide within short reaction time. The oxidative activity of this peptide is associated to the presence of a specific metal binding site present at its N-terminus. The motif is constituted by the amino acid sequence NH2-Asp-Ser-His, representing a copper and nickel amino terminal binding site, known as "ATCUN motif". The results of the study suggest that the production of reactive oxygen species can be an intrinsic property of histatin 5 connected to its ability to bind metals. (c) 2007 Elsevier Inc. All rights reserved.