Interfacial Interactions of a Myoglobin/DOPC Hybrid System at the Air-Water Interface and Its Physicochemical Properties

In the present study, the intermolecular interactionsbetween awater-insoluble phospholipid (DOPC) and water-soluble protein (myoglobin)and the interaction among themselves were investigated at the air-waterinterface using the Langmuir and Langmuir-Blodgett techniques.The effects of changes in physicochemical factors, like pH and temperature,on these interactions were also examined. Surface pressure-moleculararea (& pi;-A) isotherms of the DOPC monolayerat the air-water interface, with and without myoglobin (Myo)revealed the evolution of various physical properties, such as elastic,thermodynamic, and hysteric properties, in response to changes insubphase pH and temperature. With the increment of subphase pH from5 to 7 at a fixed temperature (20 & DEG;C), the DOPC isotherm expanded,and the in-plane elasticity (C (S) (-1)) decreased, but no significant presence of hysteresis was encounteredin either of the pH values. On the other hand, a diminution of temperature(from 20 to 5 & DEG;C) leads to an expansion of monolayers yieldinglow elasticity and significant hysteresis. The incorporation of Myomolecules within the DOPC monolayer decreased the C (S) (-1) value of the DOPC monolayer. Sucha decrement in C (S) (-1) wasalso encountered while increasing the pH and decreasing the temperature(T) of the subphase in the absence of Myo. Systematicexpansion of DOPC isotherm and increased hysteric area with the increasein Myo proportion were observed and the atomic force microscopy (AFM)observations suggested a strong conjugation between Myo and DOPC inthe mixed monolayer. The denaturation effect of Myo molecules wasstudied using AFM at different temperatures. Furthermore, the Myomolecules were found to be most surface active at pH = 7, which isvery close to its isoelectric point. These observations come up withthe interaction mechanism between biomolecules under dynamically variedconditions.