QUINACRINE - SPECTROSCOPIC PROPERTIES AND INTERACTIONS WITH POLYNUCLEOTIDES

The acridine dye quinacrine and its interactions with calf thymus DNA, poly(dA-dT).poly(dA-dT), and poly(dG-dC).poly(dG-dC) were studied by light absorption, linear dichroism, and fluorescence spectroscopy. The transition moments of quinacrine give rise to absorption bands polarized along the short axis (400-480-nm band), and the long axis (345-nm and 290-nm bands) of the molecule, respectively. Linear dichroism studies show that quinacrine intercalates into calf thymus DNA as well as into the polynucleotides, displaying fairly homogeneous binding to poly (dA-dT).poly(dA-dT), but more than one type of intercalation site for calf thymus DNA and poly(dG-dC).poly(dG-dC). Fluorescence spectroscopy shows that for free quinacrine the pK = 8.1 between the mono- and diprotonated states also remains unchanged in the excited state. Quinacrine bound to calf thymus DNA and polynucleotides exhibits light absorption typical for the intercalated diprotonated form. The fluorescence enhancement of quinacrine bound to poly (dA-dT).poly(dA-dT) may be due to shielding from water interactions involving transient H-bond formation. The fluorescence quenching in poly (dG-dC).poly (dG-dC) may be due to excited state electron transfer from guanine to quinacrine. (C) 1993 John Wiley & Sons, Inc