Nickel (II) as a temporary catalyst for hydroxyl radical generation.

Many in vivo studies show peroxidative damage during nickel toxicity, suggesting the generation of oxygen-activated species. Using the murexide (5,5'-nitrilodibarbituric acid ammonium salt) bleaching technique, we attempted to spectroscopically determine whether there are any histidylpeptides-Ni (II) complexes able to catalyze a nickel-dependent reduction of hydrogen peroxide leading to free oxygen radical production. We show that peptides containing the glycyl-glycyl-L-histidyl sequence trigger nickel-dependent production of oxygen radicals which can damage proteins, cause a rapid loss of tryptophan and a significant production of bityrosine and also induce peroxidation of polyunsaturated fatty acids. During the reaction, the histidine residue in the peptide is selectively damaged and breakdown of the peptide switches off hydroxyl-radical production.