ON THE NATURE OF INTERACTION BETWEEN PROFLAVINE and DNA

Abstract— The fluorescence decay of the mutagenic drug proflavine (PF) bound to DNA at a phosphate-to-drug ratio of 420 is found to be a non-exponential function of time. The deviation from exponentiality is shown to increase with increasing GC content of DNA. Thus, heterogeneity in the high affinity binding sites is clearly demonstrated. The nucleotides guanosine-5'-monophosphate (GMP) and cyti-dine-5'-monophosphate (CMP) are shown to form complexes with PF in 10^-3M sodium cacodylate buffer at pH 6.6. In addition, GMP quenches substantially the fluorescence of PF while CMP enhances it slightly. The fluorescence decay curves for 5 × I0^-6 M PF in the presence of GMP concentrations greater than 10^-2 M exhibit a deviation from exponentiality which parallels that exhibited by the fluorescence decay curves for PF bound to DNA of increasing GC content. It is inferred that (a) guanine is responsible for the quenching of the fluorescence of PF on binding to DNA; and (b) the forces involved in the interaction between PF and DNA are specific in nature. The implications of these findings concerning the mutagenic properties of acridine derivatives are discussed. Nanosecond depolarization studies reveal a quite fast depolarization of the fluorescence of bound PF; for the PF- Cl. perfringens DNA complex the rotational correlation time is about 26 ns. Time-resolved emission spectroscopy in the nanosecond scale demonstrates that, despite the change in the orientation of the drug, the electronic structure of the PF-DNA complex is not substantially altered during the lifetime of the excited singlet electronic state of the drug.