Search for molecular mechanisms in the genotoxicity of nickel

This paper reviews recent studies done in the author's laboratory on molecular mechanisms of nickel genotoxicity, using as an experimental model the teratogenic effects of bivalent nickel ions (Ni2+) in South Africa frogs (Xenopus laevis). A Ni(2+)-binding protein, pNiXa, was identified in Xenopus oocytes and embryos (molecular weight 45 kDa, isoelectric point approximately 8.5) with a strong homology to human alpha 1-antitrypsin, alpha 1-antichymotrypsin, and other serine proteinase inhibitors. CNBr peptides of pNiXa showed sequence identity to Ep45. Nondenatured pNiXa, purified by nickel affinity chromatography, inhibits bovine alpha 1-chymotrypsin. The possibility that pNiXa plays a key role in Ni2+ teratogenesis is indicated by (i) the avidity of pNiXa for Ni2+, (ii) the presence of pNiXa when the embryos are susceptible to Ni2+ teragenesis, and (iii) the potential of the (HX)n-motif to form Ni2+ complexes that could catalyze the formation of oxygen free radicals and thereby damage deoxyribonucleic acid (DNA) and chromosomes.