Size and molecular flexibility affect the binding of ellagitannins to bovine serum albumin. J. Agric. Food Chem. 2014, 62, 9186-9194.

Dobreva M.A., Green R.J., Mueller-Harvey I., Salminen J-P., Howlin B.J., Frazier R.A.

ABSTRACT: Binding to bovine serum albumin of monomeric (vescalagin and pedunculagin) and dimeric ellagitannins (roburin A, oenothein B and gemin A) was investigated by isothermal titration calorimetry and fluorescence spectroscopy, which indicated two types of binding sites. Stronger and more specific sites exhibited affinity constants, K1, of 104 to 106 M-1 and stoichiometries, n1, of 2 to 13 and dominated at low tannin concentrations. Weaker and less-specific binding sites had K2 -constants of 103 to 105 M-1 and stoichiometries, n2, of 16 to 30, and dominated at higher tannin concentrations. Binding to stronger sites appeared dependent on tannin flexibility and presence of free galloyl groups. Positive entropies for all but gemin A indicated that hydrophobic interactions dominated during complexation. This was supported by an exponential relationship between the affinity, K1, and the modeled, hydrophobic accessible surface area and by a linear relationship between K1 and the Stern-Volmer quenching constant, KSV.