Supercoiled DNA relaxation

These observations, together with those on supercoiled DNAs relaxed by intercalating dyes and by topoisomerase I, indicate that complete conversion from the prevalent secondary structures in supercoiled DNAs to the normal B-helix must be severely hindered kinetically. It is also clear that the free energies per base pair of the secondary structure states a and b must be nearly identical in order for these states to be interconverted by such a small environmental perturbation. 

---