RAMAN-SPECTROSCOPIC STUDY OF THE EFFECTS OF CA-2+, MG-2+, ZN-2+, AND CD-2+ IONS ON CALF THYMUS DNA - BINDING-SITES AND CONFORMATIONAL-CHANGES

The interaction of Mg2+, Ca2+, Zn2, and Cd2+ with calf thymus DNA has been investigated by Raman spectroscopy. These spectra reveal that all of these ions, and particularly Zn2+, bind to phosphate groups of DNA, causing a slight structural change in the polynucleotide at very small metal: DNA(P) concentration ratio (ca. 1 : 30). This results in increased base‐stacking interactions, with negligible change of the B conformation of DNA. Contrary to Zn2+ and Cd2+, which interact extensively with the nucleic bases (particularly at the N7 position of guanine), the alkaline‐earth metal ions are bound almost exclusively to the phosphate groups. The affinity of both the Zn2+ and Cd2+ ions for G‐C base pairs is comparable, but the Cd2+ ions interact more extensively with A · T pairs than Zn2+ ions. Interstrand cross‐linking through the N3 atom of cytosine is suggested in the presence of Zn2+, but not Cd2+. Copyright © 1990 John Wiley & Sons, Inc.