Spectroscopic investigations on the binding of persimmon tannin to phospholipase A2 from Chinese cobra (Naja naja atra)

To understand the anti-venom mechanism of persimmon tannin, the interaction between persimmon tannin (PT) and phospholipase A2 (PLA2) under physiological conditions was investigated by fluorescence quenching technique in combination with Fourier transform infrared (FT-IR) and circular dichroism (CD) spectra techniques. The results revealed that gradual fluorescence quenching was observed by titration of PLA2 (2.0 μM) with increasing concentrations of PT (from 0 to 2.025 μM), and the type of quenching was found to be a static quenching process. Stern–Volmer plots were not linear but had an intersection at CPT ≈ 1.0 μM, indicating that PT binded to more than one class of sites on PLA2. The binding sites calculated on basis of Scatchard plots were about 2, supporting this result. The enthalpy change (ΔH) and entropy change (ΔS) of the binding sites were −17.44 kJ/mol and 59.90 kJ/mol·, separately, suggesting that hydrophobic interaction played a main role in the binding. In addition, synchronous fluorescence, FT-IR and CD spectra showed that dramatic conformational changes in PLA2 were induced by its interaction with PT.