THERMODYNAMICS OF THE INTERACTION OF BERBERINE WITH DNA

The interaction of berberine ,8,13,13a-tetrahydro-9-10-dimethoxy-2,3-( methylene dioxy)-berberinium] with calf thymus DNA has been studied by spectrophotometry in buffers of various salt concentrations and tempe ratures. Binding parameters obtained are best fit by the neighbour exc lusion model. The salt and temperature dependence of the binding const ants arc used to estimate thermodynamic parameters involved in the com plex formation of berberine with DNA. The binding process is exothermi c over the entire range and the values of enthalpy and entropy change are strongly dependent on the salt concentration. The negative enthalp y and positive entropy changes compensate one another to produce a rel atively small Gibbs' free energy change. Possible molecular contributi on to the enthalpy and entropy changes is discussed.