The binding of ethidium bromide with DNA: interaction with single- and double-stranded structures

The pH-induced helix-coil transition of DNA and its complexes with EtBr is carried out at acidic pH in a wide interval of change of concentration ratio of EtBr/DNA. The binding isotherms of EtBr on double and single-stranded DNA at pH = 7.0 and pH = 3.0 (t = 25degreesC) are obtained by absorption and fluorimetric methods. Binding constants (K) and number of bases (n), corresponding to one binding site were determined. Non fluorescent strong complex with ds-DNA at pH = 7.0 and t = 25degreesC as well as strong and weak complexes with ss-DNA at pH = 3.0 and t = 25degreesC are revealed.