Characterization of the Binding of Adriamycin to Dna by Spectroscopic Methods

Adriamycin(ADM) binds to the double helical DNA with a high affinity, as deduced from the absorption and fluorescence spectral data. Extensive hypochromism, red shifts, and an isosbestic point in the absorption spectra were observed when ADM binds to calf thymus DNA(CT DNA), which suggested the intercalation mechanism of ADM into DNA bases. Upon binding to DNA, the fluorescence from ADM was efficiently quenched by the DNA bases, with no shifts in the emission maximum. the large increases in the polarization upon binding to CT DNA supported the intercalation of ADM into the helix. Iodide quenching studies showed that the magnitude of K_sv of the bound ADM was lower than that of the free ADM. the results of competitive binding studies showed that ethidium bromide could be displaced by Adm. Thermal denaturation experiments exhibited that the quenching of the fluorescence from ADM by single strand(ssDNA) was smaller than that by double strand(dsDNA). the results of all further studies also proved the intercalation of ADM into DNA base stack.