Effect of metal ions on the binding reaction of (−)-epigallocatechin gallate to β-lactoglobulin

Publication date: 15 April 2017
Source:Food Chemistry, Volume 221
Author(s): Liangliang Zhang, Indra Dev Sahu, Man Xu, Yongmei Wang, Xinyu Hu
The effects of metal ions (Cu²⁺, Sn²⁺, Zn²⁺, Mn²⁺, Al³⁺ and Fe³⁺) on the interaction between (−)-epigallocatechin-3-gallate (EGCg) and β-lactoglobulin (β-Lg) were investigated via fluorescence and circular dichroism (CD) spectroscopy. The results of the fluorescence titration experiment demonstrated that the addition of Cu²⁺ increases the quenching efficiency of EGCg to β-Lg by more than EGCg alone, while Mn²⁺, Al³⁺ and Zn²⁺ decrease the quenching efficiency of EGCg to β-Lg by less than EGCg alone. [β-Lg-Mn], [β-Lg-Al], [β-Lg-Zn] and [β-Lg-Sn] obviously decreased the apparent binding affinities (Ka) of EGCg to β-Lg by 95.53%, 81.94%, 44.66% and 38.58%, respectively, whereas [β-Lg-Cu] significantly increased the Ka of EGCg for β-Lg by 115.44%. The results of CD spectroscopy experiment showed the α-helix content of β-Lg decreased with the addition of Cu or Al, indicating that the β-Lg-Cu and β-Lg-Al interaction resulted in unfolding of the secondary structure of β-Lg.



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