Thermodynamics of DNA condensation caused by Mn2+ binding

Interaction between Mn2+ ion and the two forms of DNA duplex (supercoiled and linearized pUC119 DNA) in solution has been examined by isothermal titration calorimetry. Although DNA condensation reaction heat was observed at 323 K, this was not the case at 298 K. DNA condensation was entropically driven and supercoiled DNA was found to be more susceptive. The enthalpy of DNA condensation is estimated 0.42 kJ/mol for both DNA forms. Conversely, the entropy of DNA condensation was 0.13 kJ/mol K for supercoiled DNA, and 0.12 kJ/mol K for linearized DNA. The difference of entropy is attributable to their DNA conformation.