| Abstract: | Proflavine binding may be used as a probe of the environment and interactions of DNA. In this paper we report the effects of the divalent cations Mg++ and putrescine and the trivalent cation spermidine on the proflavine–Na DNA binding equilibrium. Difference spectroscopy at 430 nm was used to determine apparent proflavine–DNA binding constants K at several concentrations of each cation for temperatures between 15 and 43°C, and at a constant total ionic strength of 0.1M. Mg++, putrescine, and spermidine all have greater effects on K than expected on the basis of ionic strength alone in the order spermidine > Mg++ ? putrescine. van't Hoff analysis of K(T) enabled calculation of ΔH° and ΔS°, which are affected differently by each cation. These differences are discussed qualitatively in terms of such concepts as release of condensed counterions, localized or unlocalized condensation, hydration, and restriction of molecular and internal rotation. |
