Determining DNA supercoiling enthalpy by isothermal titration calorimetry

► DNA intercalators bind to supercoiled, nicked, and relaxed DNA templates with different DNA-binding enthalpies. ► DNA supercoiling enthalpy of plasmid pXXZ6, a 4.5 kb plasmid was determined to be ∼11.5 kcal/mol per ΔLk. ► The unfavorable ΔGS stemmed exclusively from a large (+) ΔHS and was compensated by a large, favorable TΔSS.