Calorimetric studies of the interaction between DNA and poly-L-lysine

The transition enthalpy deltaH of the helix-random coil transition of the DNA-polylysine complex was measured as a function of the peptide:nucleotide ratio by the help of an adiabatic scanning differential calorimeter. Furthermore the transition enthalpy of a complex with a specific peptide:nucleotide ratio was determined as a function of the cation concentration of the solution. Finally the reaction enthalpy of the interaction of polylysine with native and denatured DNA was measured with the help of a LKB batch calorimeter. From the results of the calorimetric measurements one can conclude that the transition enthalpy of the DNA-polylysine complexes is linearly dependent on the nucleotide: peptide ratio. The extrapolated value for the 1:1 complex is 14.4 kcal per mole base pairs.