The mechanism of the drug induced partial displacement of methyl green from DNA.

The displacement of methyl green, a dye bound ionically to double stranded DNA, has been suggested as a potential assay for drug-DNA interaction. The present investigation studies the equilibrium system of methyl green, its colorless carbinol form and DNA in the presence of salt (MgSO4), ethidium bromide, and quinine. The reversibility of the equilibrium, and the absence of sequestered sites or two modes of binding for methyl green are demonstrated.