A combined spectroscopic and molecular docking approach to characterize binding interaction of megestrol acetate with bovine serum albumin. 
The binding interactions between megestrol acetate (MA) and bovine serum albumin (BSA) under simulated physiological conditions (pH 7.4) were investigated by fluorescence spectroscopy, circular dichroism and molecular modeling.  The results revealed that the intrinsic fluorescence of BSA was quenched by MA due to formation of the MA-BSA complex, which was rationalized in terms of a static quenching procedure.  The binding constant (Kb ) and number of binding sites (n) for MA binding to BSA were 2.8 × 10(5) L/mol at 310 K and about 1 respectively.  However, the binding of MA with BSA was a spontaneous process due to the negative ∆G(0) in the binding process.  The enthalpy change (∆H(0) ) and entropy change (∆S(0) ) were - 124.0 kJ/mol and -295.6 J/mol per K, respectively, indicating that the major interaction forces in the binding process of MA with BSA were van der Waals forces and hydrogen bonding.  Based on the results of spectroscopic and molecular docking experiments, it can be deduced that MA inserts into the hydrophobic pocket located in subdomain IIIA (site II) of BSA.  The binding of MA to BSA leads to a slight change in conformation of BSA but the BSA retained its secondary structure, while conformation of the MA has significant change after forming MA-BSA complex, suggesting that flexibility of the MA molecule supports the binding interaction of BSA with MA.