Binding of wogonin to human gammaglobulin

The binding of wogonin to HGG was studied by spectroscopic method including circular dichroism (CD), fourier transformation infrared spectra (FT-IR), fluorescence spectra. The binding parameters and the thermodynamic parameters for the reaction have been calculated according to Sips method and Gibbs-Helmholtz equation, respectively, at different temperatures. AutoDock3.05 program was used to calculate the interaction modes between the drug and HGG. The Sips plots indicated that the binding of HGG to wogonin at 297, 304, 310 and 317 K is characterized by two binding sites with the average affinity constant Ko at 2.102 × 104, 2.078 × 104, 1.956 × 104 and 1.931 × 104, respectively. The binding process was exothermic, spontaneous and entropy driven, as indicated by the thermodynamic analyses, and the major part of binding energy is electrostatic interaction accompanied by hydrophobic interaction and hydrogen bond. The secondary structure compositions of free HGG and its wogonin complexes were estimated by the FT-IR spectra and the curve-fitted results of amide I band, which are in good agreement with the analyses of CD spectra. Furthermore, the average binding distance between wogonin and HGG (5.60 nm) was obtained on the basis of the theory of Förster energy transfer.