A microcalorimetry and binding study on interaction of dodecyl trimethylammonium bromide with wigeon hemoglobin

The thermodynamic parameters for the binding of dodecyl trimethylammonium bromide (DTAB) with wigeon hemoglobin (Hb) in aqueous solution at various pH and 27 °C have been measured by equilibrium dialysis and titration microcalorimetry techniques. The Scatchard plots represent unusual features at neutral and alkaline pH and specific binding at acidic pH. This leads us to analyze the binding data by fitting the data to the Hill equation for multiclasses of binding sites. The best fit was obtained with the equation for one class at acidic pH and two classes at neutral and alkaline pH. The thermodynamic analysis of the binding process shows that the strength of binding at neutral pH is more than these at other pH values. This can be related to the more accessible hydrophobic surface area of wigeon hemoglobin at this pH. The endothermic enthalpy data which was measured by microcalorimetry confirms the binding data analysis and represents the more regular and stable structure of wigeon hemoglobin at neutral pH.