Molecular interaction of different chromium species with nucleotides and nucleic acids

The interaction of chromium(III) and chromium(VI) with the phosphate groups of di- and triphosphate nucleotides were examined by 31P-NMR spectroscopy. Chemical shifts of the phosphate groups, indicating the formation of Cr-nucleotide complexes, could only be detected with Cr(III). When Cr(III) was generated from Cr(VI) by reduction with an excess of glutathione, nearly the same chemical shifts could be observed. This indicates that glutathione is not capable of trapping Cr(VI) by reduction with subsequent formation of stable Cr-GSH complexes, thus preventing the binding of chromium to important target molecules as DNA or nucleotides. Using radioactively-labelled chromium no 51Cr(VI) bound to any nucleic acid, whereas 51Cr(III) bound in increasing order to poly(A).poly(U), calf thymus DNA and poly(G).poly(C). Furthermore, the melting temperature of nucleic acids increased in the same order only in the presence of Cr(III). Possible genotoxic consequences in vivo of the presented data in vitro concerning the binding of Cr(III) to sensitive molecular targets are discussed in detail.