Study on the interaction of oxymatrine with bovine serum albumin

The binding reaction of oxymatrine (OMT) with bovine serum albumin (BSA) was studied by the methods of isothermal titration calorimetry, fluorescence, and circular dichroism (CD) spectroscopy. The thermodynamic results indicated that there were two classes of binding sites on the BSA molecule for OMT molecule. When the drug molecule binding to the first class of sites, the standard changes of enthalpy (Delta H (1)A degrees) and entropy (Delta S (1)A degrees) were (-1.07 +/- A 0.50) kJ/mol and (98.3 +/- A 0.50) J/mol/K, respectively. The possible largest number of binding site (N (1)) was (10.0 +/- A 0.20). This type of binding was an enthalpy-entropy synergically driven process. On the second class of binding sites, the standard changes of enthalpy (Delta H (2)A degrees) and entropy (Delta S (2)A degrees) were (1.91 +/- A 0.03) kJ/mol and (79.8 +/- A 0.40) J/mol/K, respectively. The possible largest number of binding site (N (2)) was (25.0 +/- A 0.30). This type of binding was entropy driven process. The intrinsic fluorescence of BSA was slightly quenched by the formation of BSA-OMT complex. The CD spectra experiment showed that the alpha-helix contents of BSA decreased. These revealed that the microenvironment and conformation of BSA were changed in the binding reaction.