INTERACTION OF METAL IONS WITH POLYNUCLEOTIDES AND RELATED COMPOUNDS .12. RELATIVE EFFECT OF VARIOUS METAL IONS ON DNA HELICITY

The ability of Cu(II) and Zn(II) to bring about the unwinding and rewinding of the DNA double helix under appropriate conditions has been previously demonstrated. The present study reveals that other divalent metal ions have similar effects upon DNA and can be placed in a sequence that indicates the magnitude of their influence on DNA structure, as follows: Mg(II), Co(II), Ni(II), Mn(II), Zn(II), Cd(II), Cu(II). This sequence is deduced from the following phenomena. (1) The melting temperature (Tm) of DNA increases with increasing metal concentration for the metals at the left of the series, whereas Tm passes through a maximum for the metals to the right, the maximum occurring at lowest concentration at the far right. (2) Mg(II) at the far left cannot induce any detectable rewinding of the double helix; Co, Ni, and Mn produce partial rewinding, whereas the metals on the extreme right bring about complete renaturation of DNA. (3) These metals produce an increasing shift in the absorption maximum of DNA, from left to right. The placement of the metals in the same sequence by these three criteria is readily explained by their ability to bind both phosphate and heterocyclic “base” sites with the ratio of affinity for “base” to phosphate increasing from left to right. © 1968, American Chemical Society. All rights reserved.