Thermodynamic and binding study of hemoglobin, oxy-hemoglobin and carbamino-hemoglobin upon interaction with cationic surfactants, using surfactant membrane selective electrodes

The interaction of tetradecyltrimethylammonium bromide (TTAB) and cetyltrimethylammonium bromide (CTAB), two cationic surfactants, with hemoglobin (Hb) has been studied using potentiometric technique based on a surfactant ion selective membrane electrode in the presence of 2.7 mM buffer solution, pH 6.4 phosphate and pH 8.3 glycine. Binding isotherms were obtained from the potentiometric technique and using the Wyman binding potential model, apparent binding constants were calculated. Thermodynamic parameters were obtained for binding process from the Wyman binding potential analysis. Binding of surfactant molecules induced the unfolding of hemoglobin accompanied with exposure of the heme pocket and facilitating the oxidation of heme. The Gibbs free energy change calculated on the basis of the Wyman binding potential concept decreases in the initial stages of binding and passes through a minimum, followed by occupation of the different binding set. The affinity of binding of surfactant to Hb increased with increasing temperature, indicating an endothermic and essentially entropy driven process. On the other hand, a comparison between hemoglobin (Hb) oxy-hemoglobin (O2-Hb) and carbamino-hemoglobin (CO2-Hb) upon the interaction with CTAB was carried out.