Both active components of plant herbs with an analogical isomeride structure (alpinetin and cardamonin) were chosen as research targets. A combination of intrinsic fluorescence, UV-Vis, FTIR and the molecular modeling techniques has been used to characterize the binding between both flavones and human gammaglobulin (HG). The results from fluorescence spectroscopy indicated that the two drugs could interact with the protein strongly (binding constants between 10⁴～10⁵). The two drugs indicated different quenching mechanisms (static quenching mechanism for alpinetin and dynamic quenching mechanism for cardamonin rarely). The binding parameters for the different dug-HG systems are different at different temperatures (298, 308, and 318 K), and the binding modes were also different. The values of r are lower than 7 nm after interaction between the protein tryptophan residue and the bound alpinetin or cardamonin molecules (3.88 and 4.52 nm, respectively), which indicated the efficiency of energy transfer. The secondary structure compositions of the complexes of the globulin with the drugs were estimated by qualitative and quantitative analyses from synchronous fluorescence spectra and FT-IR experimental data. The two results of molecular model studies revealed the different binding locations for the drug-HG systems.

Key words: alpinetin, cardamonin, HG, interaction