Characterization of ellipticine binding to native calf thymus DNA

The binding of [14C]ellipticine to native calf thymus DNA was studied using equilibrium dialysis. A Scatchard polt revealed the presence of high-and low-affinity binding sites in DNA, the former having a K of 4.0 X 10(7) M(-1) and an n (saturation limiting of binding) of 0.078 (1mol ellipticine/13 mol of DNA nucleotides). The forces involved in stabilizing the high-affinity binding, which has been equated with intercalative binding, were due to a combination of hydrophobic interactions and hydrogen bonding. Difference spectra of ellipticine in the presence of the polydeoxynucleotides, poly d(A-T) or poly d(G-C), showed that there was no base specificity involved in the high-affinity binding. Ellipticine binding to the low-affinity sites, which has been equated with surface binding, was due primarily to the participation of electrostatic interactions of ellipticine with the anionic phosphate groups on the double helical surface of DNA.