Abstract
It is well known that proflavine binds to DNA. Here we investigate the binding mode of proflavine to native DNA using absorption, circular dichroism (CD), and linear dichroism (LD) spectroscopy as well as by fluorescence techniques. The observed changes of proflavine upon complexation with DNA can be summarized as a red shift and hypochromism in the absorption spectrum. The negative LDr in the proflavine absorption region has a magnitude comparable to or larger than that of the DNA absorption region, confirming the intercalative binding mode of proflavine to DNA. Saturation of the LD spectrum in the proflavine absorption region at R = 0.25 and a decrease in the fluorescence intensity provide further evidence of intercalation. Furthermore, the coupling of electric transition of intercalated proflavine is observed. Although proflavine has been reported to position itself along the DNA stem at high [proflavine]/[DNA base] ratios, the spectral characteristics, which include a clear isosbestic point in the absorption spectrum and proportionality in the LD magnitude in the proflavine absorption region, do not show any possibility of exterior binding.
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