Interactions of tea tannins and condensed tannins with proteins

Binding parameters for the interactions of four types of tannins: tea catechins, grape seed proanthocyanidins, mimosa 5-deoxy proanthocyanidins,and sorghum procyanidins (mDP=17), with gelatin and bovine serum albumin (BSA) have been determined from isothermal titration calorimetry data. Equilibrium binding constants determined for the interaction with gelatin were in the range 10(4) to 10(6) M-1 and in the order: sorghum procyanidins > grape seed proanthocyanidins > mimosa 5-deoxy proanthocyanidins > tea catechins. Interaction with BSA was generally weaker, with equilibrium binding constants of <= 10(3) M-1 for grape seed proanthocyanidins, mimosa 5-deoxy proanthocyanidins and tea catechins, and 10(4) M-1 for the sorghum procyanidins. In all cases the interactions with proteins were exothermic and involved multiple binding sites on the protein. The data are discussed in relation to the structures and the known nutritional effects of the condensed tannins.

Hydrolyzable tannin structures influence relative globular and random coil protein binding strengths

Binding parameters for the interactions of pentagalloyl glucose (PGG) and four hydrolyzable tannins (representing gallotannins and ellagitannins) with gelatin and bovine serum albumin (BSA) have been determined from isothermal titration calorimetry data. Equilibrium binding constants determined for the interaction of PGG and isolated mixtures of tara gallotannins and of sumac gallotannins with gelatin and BSA were of the same order of magnitude for each tannin (in the range of 10(4)-10(5) M-1 for stronger binding sites when using a binding model consisting of two sets of multiple binding sites). In contrast, isolated mixtures of chestnut ellagitannins and of myrabolan ellagitannins exhibited 3-4 orders of magnitude greater equilibrium binding constants for the interaction with gelatin (similar to 2 x 10(6) M-1) than for that with BSA (similar to 8 x 10(2) M-1). Binding stoichiometries revealed that the stronger binding sites on gelatin outnumbered those on BSA by a ratio of at least similar to 2:1 for all of the hydrolyzable tannins studied. Overall, the data revealed that relative binding constants for the interactions with gelatin and BSA are dependent on the structural flexibility of the tannin molecule.