Binding of dihydromyricetin to human hemoglobin: fluorescence and circular dichroism studies

The binding reaction between dihydromyricetin (DMY) and human hemoglobin (HHb) was investigated systematically with various spectroscopic methods including fluorescence quenching technique, ultraviolet (UV)-vis absorption, synchronous fluorescence, circular dichroism (CD) spectroscopy. The experimental results showed that DMY effectively quenched the intrinsic fluorescence of HHb via static quenching. DMY binds to HHb with a stoichiometry that varies from 0.972:1 to 0.906:1 as the temperature increases from 296 to 304 K. The DMY-HHb binding constants were determined to be K(296)=2.79 × 10(4) and K(304)=1.18 × 10(4) Lmol(-1). The reaction is characterized by negative enthalpy (ΔH=-80.46 kJ mol(-1)) and negative entropy (ΔS=-186.72 kJ mol(-1)), indicating that the predominant forces in the DMY-HHb complex are van der Waals and hydrogen bonding forces. Based on the Förster's theory of non-radiative energy transfer, the binding distance between DMY and the inner tryptophan residues of HHb was determined to be 3.15 nm. Furthermore, the CD spectroscopy indicated the secondary structure of HHb is not changed in the presence of DMY.