Analysis of eupatilin-human serum albumin interactions by means of spectroscopic and computational modelling.

The interaction of eupatilin (5,7-dihydroxy-3',4',6-trimethoxyflavone) with human serum albumin (HSA) was studied at simulative physiological pH, with a HSA concentration of 3.0 x 10(-6)mol L(-1) and eupatilin concentrations over the range of 6.0 x 10(-6) to 1.9 x 10(-5) mol L(-1). Fluorescence spectroscopy in combination with UV absorption spectroscopy and Fourier transform infrared (FTIR) spectroscopy were used to study the binding properties (including binding mechanism, the binding constants, the number of binding sites and the binding mode) of the interaction of eupatilin with HSA and the effect of this drug on HSA conformation changes. According to the Scatchard equation there was only one class of binding site that could bind to HAS; the binding constants were 1.53 x 10(5), 1.20 x 10(5), 1.05 x 10(5), 0.87 x 10(5) L mol(-1) at temperatures of 287, 298, 310 and 318 K, respectively. The FTIR spectra revealed that the protein secondary structure changed, with reductions in alpha-helices of about 3.65% at a drug to protein molar ratio of 3. The thermodynamic analysis (enthalpy and entropy change: DeltaH(0) and DeltaS(0)) and the computational modelling study indicated that hydrophobic force played an important role in eupatilin-HSA complex stabilization, and eupatilin could bind within the subdomain IIA of HSA.