A steady-state and time-resolved fluorescence, circular dichroism study on the binding of myricetin to bovine serum albumin.

The binding mechanism of myricetin (Myr) to bovine serum albumin was investigated by using steady-state and time-resolved fluorescence and circular dichroism. The results of the steady-state fluorescence quenching experiment indicate that it is a static quenching process (C(Myr)/C(BSA) < or = 3) at low quencher concentration and the binding site is located near the Trp212 residue. The association constants at the different temperatures were calculated. From the thermodynamic parameters, enthalpy change (DeltaH(0)), Gibbs free energy change (DeltaG(0)) and entropy change (DeltaS(0)) obtained in the experiment, it was found that hydrophobic and electrostatic interactions play important roles in binding Myr to BSA. According to the Föster energy transfer theory, the separation distance, r, the energy transfer efficiency, E, and Föster radius, R(0), were calculated. The results obtained from the above experiments indicate that Myr can be tightly bound to BSA. Then, the effects of ionic strength, metal ion, pH and surfactants on the binding Myr and BSA were investigated, which also showed that electrostatic and hydrophobic interactions play a major role in the association process. On the other hand, the conformation and secondary structure of BSA were further studied through circular dichroism and fluorescence synchronous spectra. It was found that the conformation and secondary structure of BSA had also changed after interaction with Myr. The time-resolved fluorescence study showed that the short lifetime of BSA decreased after the addition of Myr, which implies that the buried Trp 212 is the main binding site.