Abstract: Interaction of mitoxantrone and deoxyribonuleic acids was studied at different phosphate/drug ratios(P/D), and it was found that there are two types of binding processes and interaction models. In a certain range of P/D, one type of model is dominant. At P/D <3, MX leads to condensation of DNA. At higher P/Dratio, MX intercalate into DNA, leading to red-shift of absorption spectra. At P/D>6, MX and DNA are in the binding e-qulibrium, the equilibrium binding constant of MX and calf thymus DNA is 9. 0×10⁵(mol/L)^-1at 20℃, and the binding site size n is 5. The results indicate that major groove and minor groove may be the most favorable binding sites in the structures of double stranded nucleic acids. There existed anticooperative effects between the binding sites.

Key words: Mitoxantrone, DNA, Binding equilibrium, McGhee and Von Hippel equation