A microcalorimetric study on the binding of proflavine with tRNAphe

The interaction of proflavine with tRNAphe was studied using isothermal titration calorimetry to gain insights into thermodynamics of the binding reaction. Isothermal titration calorimetric studies revealed the association to be exothermic and favored by both negative enthalpy and positive entropy changes. The equilibrium constant for the complexation process was calculated to be (2.85 ± 0.09) 105 M−1 at T = 293.15 K. The equilibrium constant decreased with increasing temperature suggesting that the complexation is less favored at higher temperatures. The standard molar enthalpic contribution enhanced in magnitude while the standard molar entropic contribution decreased with increasing temperature. The complexation was further characterized by negative standard molar heat capacity and (enthalpy + entropy) compensation. Salt dependent ITC studies and parsing of the standard molar Gibbs energy revealed that the complexation process was largely dominated by non-polyelectrolytic forces which remained almost unaltered at all the salt concentrations studied.