| Abstract: | The binding of methylene blue, proflavine, and ethidium bromide with DNA has been studied by spectrophotometric titration. Methylene blue and proflavine or methylene blue and ethidium bromide were simultaneously titrated by DNA. The results indicate that all of these dyes compete for the same bindine sites. The binding properties are discussed in terms of symmetry. The optical properties of the dye–DNA complexes have been studied as a function of DNA/dye ratio. The induced circular dichriosm due to dye–dye interaction was measured at low dye/DNA ratios for cases involving both the same dye and different dyes. A positive Cotton effect for DNA–proflavine complex may be induced at 465 mμ by eithr proflavine or ethidium bromide, whereas a netgative Cotton effect at 465 mμ may be induced by methylene blue. The limiting circular dichroism, with no dye–dye interaction, and the induced circular dichroism spectra are discussed in terms of symmetry rules. |
