Interaction of DNA with heavy metal ions and polybases: cooperative phenomena.

Abstract

AbstractThe polarographically determined binding constants of Cu++ and Cd++ to DNA were found to decrease with the degree of binding. The binding causes a reduction in the electrostatic potential ψ on the DNA molecule. The binding constant conforms to the relation K = K0 exp {‐zeψ/kT}. The binding constant at zero potential K0 depends on the nature of the competing counterfoils to the phosphate group of the DNA; it is apparently smaller when Na+ rather than the ethylpyridonium residue of polyvinylpyridine serves as the competing counterfoil. The specific interact ion between the ethylpyridonium residues of the polybase and the DNA is very weak, even though the polyelectrolytic interaction induced by the decrease of the electrostatic free energy is spectacular. The intereaction is reversible and equilibrium is maintained between the different interaction products. A reshuffling of the interacting partners can be effected by spontaneous or induced (by centrifugal forces) precipitation of the least soluble interaction products participating in the equilibrium.