The interaction of oxymatrine (OMT) with bovine serum albumin (BSA) was investigated by using nano-watt-scale isothermal titration calorimetry and circular dichroism (CD) spectrometry at 298.15 K. Changes of thermodynamic functions corresponding to the binding process were obtained and discussed. The results indicated that there were two classes of binding sites between BSA and OMT molecules. When the drug molecule binding to the first class of sites, the binding constant the standard changes of enthalpy and Gibbs free energy are (2.14±0.31)×105, (－1.07±0.50) kJ•mol－1 and (－30.4±0.4) kJ•mol－1, respectively. The possible largest number of binding site (N1) is (10.0±0.2). This type of binding is an enthalpy-entropy synergically driven process. On the second class of binding sites, the binding constant the standard changes of enthalpy and Gibbs free energy are (6.84±0.32)×103, (1.91±0.03) kJ•mol－1 and (－21.9±0.4) kJ•mol－1, respectively. The possible largest number of binding site (N2) is (25.0±0.3). This type of binding is an entropy driven process. The CD spectra showed that both the conformation and the relative contents of secondary structure units of BSA were changed by the two types of binding processes.

Key words: isothermal titration calorimetry, circular dichroism spectrometry, oxymatrine, bovine serum albumin