Study of ethidium bromide interaction peculiarities with DNA

The helix-coil transition of DNA-ethidium bromide complexes in an interval of ionic strength of 2.0 x 10(-3) M less than or equal to mu(Na+) less than or equal to 2.0 x 10(-2) M has been investigated. It has been revealed that at the certain high ligand-DNA ratios (r(b)) the transition interval of the complex - (DeltaT) becomes equal to that of DNA itself (DeltaT(0)). It has been shown that the values of rb at which deltaDeltaT=DeltaT-DeltaT(0)=0 depends on ionic strength of a solution. Further increasing of ligand concentration leads to its conversion from stabilizer into the destabilizer of the double-stranded DNA.